Indian Railways - No refund for diverted train

I booked three tickets in AC *st class is Udyan express from Mumbai to Bangalore on **th August. The train was cancelled at the source station (Mumbai) and it was diverted to start from Solapur, due to which we did not travel in it. Since I was travelling with a pet and my family members, which includes a senior citizen in it, I had to book another ticket in the different train which we booked in Coimbatore express on the same night from different substation of Mumbai (Lokmanya Tilak terminus).
When we arrived in Bangalore after all the hassle I waited for * days that I should automatically get a refund for the diverted train when I did not receive any refund. I spoke to customer service. They refused to refund saying that I should have filed a TDR within ** hours of actual boarding time of the train. I requested them through email for a refund because I was travelling on another train and the original train was cancelled at source station, they aren't ready to understand.
If they have such rule that they won't refund when we file TDR after ** hours, shouldn't they automatically refund for cancelled trains automatically or shouldn't they inform us ** hours prior that the train will be cancelled, the last-minute announcement was such a hassle. I should be eligible for compensation but I am only demanding my refund of ticket amount on which I have not travelled at all.
I have proof of tickets that I travelled on another train on the same date and another train was booked on the same day also.