An immovable property cannot be transferred by a power agent on the basis of unregistered power of attorney deed in his favor.
The POA deed whether registered or not, is not a title document hence the value of stamp paper used for POA deed is absolutely not a crieteria for transfer of property.
If you hav a sale agreement, even unregistered, you can file a suit for specific performance of contract by which the court would provide you at least an alternate relief of refund of your money or investment.
This being purchase of SRA, which cannot be sold within 10 years from the date of its allotment, you cannot even get it transferred to your name at this stage if 10 years period is not over, especially no agreement is valid when it is entered into within 10 years of allotment, similarly the POA deed is also not valid in law.
You may consult a local advocate with all relevant papers/documents who may suggest you some useful tips and ideas to retrieve the property by some means.