Filing a case against a bank for violating an agreement to reduce the interest rate

Hi,

I have a mortgage with a bank in Dubai. I renegotiated the interest rate with them in DEC 2018 to 4.15%. I discovered, in Jan 2020, that the bank had never amended my interest rate to 4.15% but was instead charging 7.75%. This bank has never ever sent me a statement of my mortgage.

I have been in discussion with them ever since but they are refusing to abide by the terms of that signed agreement which I have in my possession.

I want them to refund me the amount that I have been overcharged over the past 15 months. They are instead offering me a 3.99% rate for the next 3 years.

I have filed a complaint with the Central Bank, they have not replied to the Central Bank's query in the 14 working day period. The bank has told me that I can call back on Sunday to see if they have replied.

How can I get this bank to honor the agreement and refund me for their mistake? It seems that there is no accountability expected from them and I'm bearing a heavy financial burden as a result.