Gst on advance payment to builder before aggrement

Hi All,

I really need expert advise ASAP on my issue.Really appriciate quick response.Thanks in advance.

I had booked shop & paid certain amount to builder via cheque.On 20th of July,2018,Builder got advance amount in his property account.After 15 days that is 4th of Aug ,due to some unaviodable reason i have to cancle my shop booking.Now when I am asking for refund to builder,he is saying that he already paid 12% GST on advance amount & he will not refund that amount.Please be noted that no aggrement was done or any booking form filled.I would like to know whether really GST is applicable on advance amount paid to builder.If he really paid ,is there any way i can get that back or i can tell the builder that i can get that as i am canceling deal.I don't have expertise on such issue so I feel builder is taking advantage of that by saying anything.

Please advise.Thanks.