HDFC Credit cards - Hdfc credit card settlement not done properly by the bank

I started using HDFC Credit card since **** and my card expired in **** when I was in Bangalore and I was told that the new card has been sent to my Bangalore residence but I never received it. Since then I have been making payments without even having a card with me.
Having said that we had a severe financial downfall since ****, so we opted to settle the card in **** and went for a settlement wherein we gave * post-dated cheques to HDFC bank and they agreed to auto debit Rs. **** every month.
Once the tenure was over we asked them for the closure letter and they are saying the card has not been settled and we have to go in for resettlement. Also, they say that they haven't presented one PDC cheque and because of their fault we have to start from the beginning. This is truly unacceptable. My father at the age of ** went to their bank in Aminjikarai in Chennai and no one bothered to meet him in person and they communicated the aforesaid over the intercom.
We are ready to make the missed out payment (* month = Rs. ****) and we want them to issue a closure letter. Can anyone please help us out? We are getting repeated calls from one person or the other from the bank and they don't even bother to resolve this.