Goel Ganga India Private Limited - GST excess collected and not refunded back

I, Prashant Ramnath Karekar purchased flat from the builder Goel Ganga India Pvt. Ltd., in there project Ganga Legend situated at Bhavdan, Pune. The agreement of sale was carried out on **/**/****. During that period the applicable gst rate was *%. This was as per the notification no */**** – Central Tax (Rate) applicable from **th January **** sub item (da) and (db) in the Table against serial number *, in column(*) in the rate notification of **/**** and **/****. The rate applicable under the table is *% CGST, so combine **% GST and the effective rate after considering */* for land comes to *% GST.
Since this notification came, and my claim was fitting under the CLSS scheme under Pradhan Mantri Awas Yojana for Middle Income Group -* (MIG-*), I planned to buy a flat. Accordingly when the flat was purchased and loan for the same was carried out in month of March, **** informed the builder and also the banker Kotak Mahindra Bank Ltd., about buying the same under the MIG-* scheme of PMRY. But the builder once the agreement of sale was carried out issued the bill at the rate of **% GST. Which we opposed to them and after lot of meeting and discussion it was decided on **/**/**** between the builder and me that the additional *% ie., difference of ** and * will be paid to builder as deposit and the same will be refunded to me once the sanctioning authority of PMRY scheme sanctions my application. This I had to do in compulsion since without that the builder was not ready to give possession of flat and my banker had already transferred the amount to builder on sanction of loan.
I received the letter dt. **th December, **** from Kotak Mahindra Bank Ltd., my housing loan banker that my application being sanction by National Housing Bank. Accordingly we have submitted the letter to the builder M/s. Goel Ganga India Pvt. Ltd. The GST number of M/s. Goel Ganga India Pvt. Ltd., is **AAGCG****B*ZS.
But now the staff at M/s. Goel Ganga India Pvt. Ltd., are not ready to give refund of the same amount. Also they are not ready to give in writing any reasons for the same.
On **th December ****, I personally went to Pune Office and meet the concerned officer Mr.Kiran Kumar Devi ( CEO) after long discussion he assured we will refund you the money after filling the refund with the GST authority.
But then the Covid problem arised and I could not go and meet him. So I gave a call Mr. Kiran Kumar Devi, he again not ready to take the matter and informed that he do not look after the matter and others are saying we can refund.
This shows that they don’t have any intension of refunding the money. They are not giving any thing in writing or reply to emails also.