Mettel Metropolitan Telecummuncations Cancelled service but company still continues to bill me New York, New York

I switched my service from mettel to another phone company on March 29, 2010.  I called them on the 30th to cancel service and was told I couldn't cancel until they investigated to make sure I switched.  2 weeks passed and they called to tell me I was still on their "platform".  I called the new phone co. and they confirmed that I was with them and Mettel said, they would have to investigate it again.  2 weeks later another call telling me I was still on their "platform" and they would still charge me.  Strange thing is, I ordered additional services with the new company and as of the 29th, they were working on my phones, so I knew I was with the new company.  I called Mettel a third time, and was told they would have to investigate it (where have I heard that before?) and now a month later, I am paying two phone bills for the same line and Mettel will not let me go.  I have no contract with them and I have cancelled with them three times now and they still continue to bill me and now tell me I'm past due (first time in my life I've ever been past due on a bill).  I am so fed up, but do not know what I can do about it.