T-Mobile Fraudulent practices of T-Mobile Internet

Last year, my contract expired with T-mobile. I called them and asked to be switched to "pay by the minute". I only use my cell phone for 200 - 300 minutes a month. When I spoke to their representative, the first words out of my mouth were "I don't want a contract". She assured me that I would be month to month. She said that they had a plan that charged $19.95 per month for up to 300 minutes. I questioned her as to if this was a contract and she assured me that it was a month to month plan. I agreed and for the next year, I did not notice any problems. However, in July 2012, I decided to go with another carrier. I started receiving harassing phone calls from T-Mobile made by a computer 4 - 6 times a day, everyday. I finally called the company to see why they were harassing me. I was informed that I owed for one year on my contract. I explained my position and that I never signed any document agreeing to a contract but was told that the employee fraudulently enrolled my in a contract without my permission. But he also stated that there was nothing I could do about it. I wrote T-mobile management asking to see the contract but was informed "that according to their records, I had a contract" but failed to produce any documentation written or oral to substantiate their position. Since then, I have been contacted by a collection agency or so they claim and contacted by a man professing to be an attorney. So far, I have ignored their correspondence. Any ideas??