Denial of SBI RACPC to issue conditional NOC required for agreement of property mortgaged to them

My wife is a govt school teacher in kolkata. She wants to buy a flat with home loan. The flat is mortgaged with SBI RACPC South. The owner of the flat signed a MOU with the purchaser & with the same he applied for a NOC from SBI unless which he cannot enter into a valid sale agreement with the purchaser. Now, the seller, went to the bank yesterday for getting the NOC. Bank has to declare that they do not have any objection subject to clearance of all dues. As the property is mortgaged with the bank, hence sale agreement will not be valid unless SBI gives a conditional NOC. Bank clearly denies to issue NOC & forces him to repay all dues & get the No Dues Certificate. Seller is in such a financial condition during covid pandemic that he cannot collect the huge repayment amount right now. For the same financial issue, he wants to sell his property But Bank is not listening to the seller problem Without the NOC, we cannot enter into an agreement & without a sale agreement, bank loan cannot be applied. Hence the process is getting delayed. Hence, considering the fact, I want reasonable solution for purchase the flat.