stamps.com Continued to be charged after canceling Internet

Tried to cancel my service months ago but continued to be charged $15.99 a month. Luckily the credit card on file expired and they were unable to charge my credit card.  I called again to cancel the account formally.  The person on the phone would continue to give me the run around to keep me from canceling my account. He was extremely misleading.  I can see how when people call to cancel, they might not actually be canceling with the tactics their customer service personnel use.  I have an available balance to purchase postage yet he still wanted me to pay an additional $15.99. Keep my outstanding credit.  I've already paid $15.99 a month (for many months)and for nothing!  This is a ripoff!  Everyone should just use the USPS online service, which is FREE and shipping rates are discounted to keep people from waiting in line at the post office.