Timeshare rip off

I signed a timeshare contract with Playa Del Sol that states you can cancel within 5 business days. I sent cancellation letter through registered mail within the 5 day cooling off period, exercising my right to cancel. They refuse to honor my request stating my letter of cancellation did not reach them within the 5 days (they were also notified through calls of my intent to cancel). Also, I was informed by their sales representative that a registered letter dated before the 5 days cancellation period must be honored by Mexican law. I have been back and forth with this resort attempting to resolve this situation. I have filed with Profeco (they are currently working on my case) and enconsumer.gov. I have followed their law yet refuse to return my downpayment and cancel the contract. Is there anything you can do to help? Please advise. This has been going on since 8/05