Maintenance Charges Prior to Possession

The possession date of my flat was Dec 31, 2016. But builder delayed possession by 1 year. In Nov, 2017, Builder raised some undue demands that I refused to pay. The possession was put on hold. I moved to UP-RERA on Feb 15, 2018. Then the Builder called me for a meeting that was held on 24th Feb, 2018. After deliberate discussions, the builder asked me to make the payments as agreed upon in the meeting and I was assured that they would issue the Possession Letter hand-to-hand after the payments are made. On 27th of Feb, 2020, I made all the payments as agreed in the meeting. But they started to shying away from handing over possession. I wrote several emails and made various visits to their office but all in vain. It lasted for around two and half month after the payments were made (inclusive of 2 years maintenance charges) Then they called me on 17th of May, 2018 for a settlement towards UP-RERA case. The settlement was done on 17th of May, 2018 and Possession was handed over on 20th of May, 2020. Accordingly, my two years maintenance charges paid are valid till 19th May 2020 (starts from 20th May 2018). Now the builder has started charging maintenance charges from April 1st, 2020, (1 month 20 days back date) What can I do, please advice.