Paid up letter

Hello, I opened account at jet, there was a time I couldn't pay in time and u was blacklisted. Paid up the account fully in April 2021, the account have been closed now , but the problem is that I needed a Paid up letter so I can remove my name from ITC . It's been 8 months now ,they telling me that they will send my Paid up letter but nothing cming out. They handed over my account to shabiri shake collections even when the account has been closed and its reflecting on their side that irs been paid up fully. Shabiri shake dept collectors calls me almost 2 to 3 day a week telling that I must pay my credit,of which it has been closed ,I explain the same thing every time they call and simultaneously I call the JET requesting for the Paid ip letter so I can forwad it to their own dept collector. I don't knw what to do anymore because I cannot even sort out my problems because of the letter.