Audi Service Thane - Faulty Service leads to Major Engine Damage

Our main issues are as follows:
*) We started facing engine misfire one month after Feb **** when the engine overheated after Audi Service Thane's negligence during coolant tank replacement.
*) We have been repeatedly visiting them over the past * year, for engine misfire issue and coolant leak, to solve which they have changed many parts but did not check the engine gasket or do a proper diagnosis, which has led to engine head damage.
*) The car is now with them since **nd April ****. We have been asking for system log to verify from when this problem has been there and does it coincide with the improper work done by them in Feb **** during coolant tank replacement. They are dilly dallying and not answering our queries.

Case History:
**/**/****:
Audi Service Thane during a *** degree check reported that one coolant tank hose needs replacement as it is a little loose, they then replace two hoses and the coolant tank.
After taking delivery of the car post this work, on our way back home after about *-* KMs, we got “temperature too high” warnings telling us to pullover and stop driving. On inspection, we saw coolant all over the bonnet and windscreen. Looking inside we saw one of the newly replaced hoses had come undone, causing coolant shortage and engine overheating, so we called the advisor. A technician came on a bike to fill up * litre of coolant and *.* litres of water, and closed the lock of the hose which had been missed by the Service team before delivering the car to us. .
This was the first and only time we have ever received an engine/coolant overheat warning.
**/**/****:
Occasionally, we started facing some issues while switching the car on, it was like the engine was struggling to fire up and it was vibrating. In a couple of days we got an engine warning & coolant level warning.
**/**/****:
We took the car to the workshop. They told us engine oil is leaking from some parts.
*/**/****:
We visited the workshop again, with the engine starting problem having worsened.
This time we were given an estimate with a lot of new additions such as injectors and spark plugs (approx amount rs *.** lacs), We got the work done.
**/**/****, we received the car but still faced the engine start issues.
**/**/****:
The car had been to the workshop again for engine misfire and a spark plug was changed, but the misfiring on engine start and warning lights coming on remained.
From this time till March ****, we kept getting Engine misfire and Check engine warning light every now and then for which Audi Thane workshop could not give us any solutions. They would conveniently remove the warning lights.
In March ****, we were back at Audi Thane
We received an estimate for replacing the thermostat, water pump and two bottom hoses which were not replaced when the coolant tank was replaced. We were pretty upset that the entire coolant setup was not checked when we had been in the workshop so many times and coolant work was originally done in February ****. We were assured by the workshop manager that this time everything will be checked and completed to fix this coolant leak problem. He also assured us that the coolant leak is definitely not related to the engine misfiring issue. Anyway, we got the work done and took delivery by the end of March.
*/**/****:
We had another coolant warning, we filled with water as suggested by the service advisor, but still had the check engine light show up so we went to the workshop. They topped up the coolant and removed the warning lights.
Same thing happened on **/**/**** and we were back at the workshop again. We were told to keep driving until the next warning comes up, when the technicians will “take a Proper look”. Again, not something we wanted to hear after * year of complaints of the same issues.
**/**/****:
We decided to leave the car at the workshop and requested another proper inspection since coolant was still leaking somewhere and the engine issues were now persistent. In fact, now the engine was coughing and dragging while driving for the first time ever making the car unroadworthy.
**/**/****:
We get a call saying that the engine head seems to be cracked because of which the coolant is leaking. We strongly contested this possibility as by now we knew that this problem started when the car overheated because of faulty work by Audi Thane in February **** and the technicians are now just cooking up stories. We went to the workshop, the senior technician told us that the pressure test did not reveal anything, and that they “luckily” checked under the spark plugs where they found coolant in the combustion chamber.
On our asking them that how have we been missing this check since last one year, the manager who assured us that coolant leak will be completely looked after by them at the previous visit in March **** and that the coolant and engine issues were not related sat in front of us and told us that they did not feel any need to check the gasket or the engine head as it has nothing to do with coolant leak and engine misfire and that the car has probably had this gasket leak / cracked chamber for years and they have no responsibility in this issue.
Since **nd March, the car is at Audi workshop and they are not willing to accept their fault whereas we are clear that engine misfire issue started after the faulty tank replacement done in Feb ****. They have given us an estimate of Rs. *.** lacs to replace engine head and it's gasket.
We have asked them to give us warning history from the car's computer log which they are dilly-dallying.