You my be living in the said property continuously but there is no registered sale deed on your name to prove your clear and marketable title to the property.
The GPA deed is not the title deed.
The person who purchased this property by a registered sale deed cleverly and cunningly planned to avail loan from bank by pledging the property documents as collateral and defaulted the loan intentionally because he had no intention to repay the loan.
He knew that the bank will automatically take action to recover the loan amount by attaching the proeprty and bringing it to auction sale. He knew that the bank may not be able to cannot be evicted so easily as you reside in that property for over three decades.
However you must understand the fact that you are neither a owner nor a tenant in that property and as far as bank is concerned you are an unauthorised occupant in that property which has been mortgaged by the property owner for a loan amount.
You may consul a local lawyer and take legal steps first to stop the bank from taking physical possession of the property by obtaining a stay order from high court by filing a writ petition.
Simultaneously you can file a declaration suit to declare your title based on adverse possession