Billed for cancelled extras on account.

I have cancelled the extras on my account in November 2015. Thereafter I received a statement and again they billed me. I went in store on December the 7th to complain and find out what the problem was. The cashier told me to fill out a cancellation form. I completed the form and left feeling confident that all these extras will be cancelled. At this time, I already had to pay for another months extras even after I cancelled it. Earlier this week I received my statement. Still not cancelled. 3 months of extras I have to pay for. Went to the store to question why am I still getting billed. No answer from any of the cashiers. I asked her to look for the cancellation document I filled in early Dec. She couldnt find it as they have no filling system. Left my contacts so that she can call when she found it. On Friday she called. She found the paper, with my signature and adds that it was never faxed through. Also, the paper doesnt have a date on it so they can not scratch the extras but will cancel it now. I find it unacceptable. I am billed for the extras for 4 months because they failed their work. No excuses, no way of trying to compensate, a simple 'Sorry we cant write it off'!