Cancelled Mexican timeshare within 5 days via registered letter.

I purchased a timeshare in Cancun and cancelled it within the 5 days in writing (registered letter). My credit card company has refunded the down payment (contingent) , cancelled the card and has sent the merchant bank the refund request. The timeshare company still refuses to cancel and has not agreed to the refund. They call about once per week but I have not answered or returnred their calls. Should I be answering their call? I am sure it will be a reiteration that I cannot cancel the contract.