GST refund for cancellation of under construction flat

Dear Sir,

I had purchase an under construction flat from a builder in June 2022. While purchasing the flat, I paid applicable GST as flat was under construction.

Now I have option to upgrade the flat into a bigger one from builder. Builder is advising me to cancel the old agreement and make a new agreement for the new flat. Only difference in price, he is requesting.

The building has recently received OC from the authorities and GST is not applicable for the new flat.

Query is :

1. Whether I can claim refund of paid GST post cancellation of the old agreement with the builder, as there is not transfer of goods / services.

2.  If yes, what is the procedure to claim refund for this GST?

Thanks