A. First you need to verify the GPA as to whether it was registered or not? And was there any clause to permit alienate/Sale the property?
B. Secondly, whether GPA holder is still alive or not? if GPA executor died that the GPA will be inoperative. However, it has a exception to the General Rule is that if the executor executed a GPA by creating an interest over the property that GPA never become inoperative even the executor died under the Section 202 of the Indian Contract Act. Example: A is the owner, B is the GPA holder for A and B executed a Sale Agreement by receiving advance money from the purchaser, later A dies, but GPA would not end because B already created interest over the property.
C. In case if your 50% property is coming under Sy.No.45/3 as per the legal records, you can file a case against your seller and claim the damages including compensation under the indemnity clause as mentioned in the Sale Deed ( Court will award compensation even if had no indemnity clause).
D. Issue a legal notice to your seller to clear the issue and inform to the owner of Sy.No.45/3 with respect to the same. In addition, make your point under the bonafide purchaser ground and contest the case before the court and don't pay any money to the owner of Sy.No.45/3 unless get clear clarity from your seller.