Chartered Bank — Harassment by Chartered bank

I am holding a Gold Credit card with the Standard Chartered Bank for the last nine years.It is life time paid card. Recently I made a purchase with the credit card .When the Statement came through my e-mail account, without waiting for the hard Copy, I made the payment through a cheque through a Cheque collection box at the Gariahat branch of the bank. The cheque was not encashed.After a while, I received another statement saying I have defaulted in Payment. It also asked me to pay at a enhanced rate with interest etc. When I contacted the helpline, I was advised to ask the bank to stop payment on the earlier cheque and to pay a cheque for the exact amount of the purchase ( I was assured that the interest etc will be waived). Even, then I paid the full amount of the statement as I had already made a cheque for that amount. I was told by a bank Officer, the extra money will remain credited to my account.
I was reminded by a SMS that my earlier cheque has been received .As there was stop payment on this cheque( as advised by the Helpline) , naturally the bank did not make the payment. Now, I have been asked to pay a steep cancellation charge for the Stop payment cheque. Again, I contacted the Helpline and narrated the above facts. I was told that the Bank cancellation charge will be waived and I do not have to pay anything. I asked them to confirm it by a SMS .I was assured that it would be done within three days. Now, more than a week is over, and I have not received any confirmation. On the other hand , I have received a hard Copy of the Statement asking me to pay the cancellation charges of the cheque, which was misplaced by the Bank itself and not by me.
Is this the Service which is expected from a Reputed bank like Chartered Bank ?
Please advise me what should I do.