Original sale deed lost by loan issuing bank

I had taken Home Loan from SBI in 2008. I repaid the same and received the NOC from branch in Feb-18. However, when I went to collect my original papers from RACPC, Janakpuri, New Delhi, in Mar-18 they could not find/ locate my original Sale Deed in their custody. The AGM of the office has assured us that he will look into it and requested for time till 1st week of Apr-18. I have formally documented this and sent to him. There is a small background/ history to the same issue. Sometime in Jun-16, while on a visit to SBI, RACPC, Sansad Mar, New Delhi (to enquire about possibility of reducing interest rate) I wanted to check, out of curiosity, whether all my documents are in place (as I was contemplating to close my Loan A/c by prepaying the balance in the near future). To my utter surprise they couldn't locate the same document. I did a sustained follow-up with my loan issuing branch & RACPC (and also sought help from DGM, Customer Care) and I was told that the papers have been found. I requested them to respond to my numerous letters/ communication & confirm what they verbally told over phone. When they didn't, I documented all the facts and submitted to them with a closing statement that I was considering that the issue was resolved (this was sometime in Dec-16). I never got a formal response back from them. Need advise on what I should do now. I am really really worried.