Proactiv Solution Continued to bill me after I cancelled account due to timeliness of shipments Des Moines, Iowa

I placed an order for this product in November of 2011.  The first shipment arrived on time, but was much smaller than advertised.  Shipment was a one month supply.  The following month, I was billed for shipment as stated, but did not receive.  I called the company and was told " well Ma'am the next shipment is for 90 day supply and always takes longer to ship".  Shipment arrived so late that I had run out of product.  So I called to cancel my subscription and was told I had a balance of $36.  I do not understand since I have been billed 4 times since I cancelled.  Once for $32, and 3 times for $19.95.  I have only received the initial 30 day supply, and then the late 90 day supply.  When I contacted the company, they said I am being billed since I did not return the product.