Market Leader Erroneous Billing and Rude Unhelpful Employees Bellevue Washington

I cancelled my Market Leader Pro service in Mar 2014.  In April they billed me.  I disputed the payment on my credit card.  Then I started receiving phone calls from Market Leader billing trying to recover the April payment.  I told them I had cancelled the service back in March.  May come and they bill me again, which I dispute again.  Once again I tell them I have cancelled the service, but this time the billing representative becomes very aggressive with me and tells me they will continue to charge me and pursure payment from me.  June comes and yes, I was billed again, disputed again and I am receiving calls from Market Leader trying to collect the payment.  I am no longer taking their calls as I have responded to them multiple times in writing and on the phone.  The employees don't care what you have to say - there was no attempt made from billing to verify that my service was cancelled or follow up on what may have gone wrong on their end with lack of communication.  My fear now is they will turn this over to a collection company.... Let the battle begin.