Need help with building assoc dispute

Hi friends, So we’re In a dispute with our building association over payment of maintenance money for one time last year. We don’t live there all the time so my dad has forgotten to pay the amount before deadline a couple times but they issue a small fine and we pay that as well. Last year when we were in Chennai my dad went to pay in the office, the accounts guy took cash and told him they’d send the confirmation later and they have sent it later. Fast forward Few months later they informed my dad that amount is still due and now it has accrued interest and that interest has interest as well. They are saying they made a mistake and accidentally marked someone else’s payment as ours. My dad raised a dispute with the assoc but they have investigated it themselves and said it’s some error so we still have to pay it. Last September when we were in Chennai they even cut power and haven’t given it back since. We actually had to stay in a relatives house for 2 days due to this even though all other amounts have been paid. From what I’ve researched online it’s illegal to cut power like that. my dad also says it’s illegal to charge interest over interest and they’re also blaming us for their mistake. I’d like some advice regarding this situation and especially getting power back. My dad survived Covid and has had some other health issues which has kinda diluted his mental strength and strong personality. I’m trying to help him sort this issue out. Thank you