Discussions

I wanted to cancel my gym membership and phoned and spoke to two different staff. They both told me to just put it in writing and submit it to them. I did just that, and threw it in the mail because I was leaving town for a a little while and wouldnt have time to drop it off before I left. I called about a week later and they said they had the letter.  
Now, the beginning of the month, I got charged again for my membership. I called them and they claim they never saw the letter, and the staff I talked to that did say they had the letter, is no longer working there.  
They say there is nothing they will do about me being charged this month, will "try" and cancel for next month.  
What should I do? My work schedule doesnt allow me any time to go, and I dont want to be paying for it.