Hitachi split inverter AC 1 - AC breakdown due to leakage

I have purchased my Hitachi AC long * years back then and did a re installation from Hitachi itself which they have a collaboration with johnson so my ac was installed from an old place to new place in the month of November **th **** and from since then we didn't operate the AC as it was winters and now when the summer arrived it has hardly been three months and my ac is not cooling so I got a technician who visited again from Hitachi billed me ***rs just to say that there is a leakage after seeing from outside itself and now they are asking me to give **** rs to fill nitrogen gas and to find the leakage where I asked them that how did it happen where the technician told me verbally it was the re installation guys fault he didn't re install it properly and when I said the same to the technicians manager then she is saying me that after top-up of nitrogen gas it has a validity of three months whereas I didn't top up any gas itself in the reinstallation process the gas was adequate and now they are simply refusing and telling that you need ****rs to fill up the gas and find the leakage so we need the machine tool up to our warehouse.I need help as this is a issue of faulty reinstallation which resulted in my ac breakdown