N. E. M. I ordered tomato plants and receive a call about getting a free $2 bill and the other one that came with if I didn't want it I could send it back and cancel. I am still receiving them and being charged Wallingford, Connecticut

I ordered tomato plants.  I received the plants and was charged for them.  I received a call about 2 weeks before I received my plants stating that I was receiving a $2 bill for free and there would be a second one that I could purchase if I wanted to or I could send it back.  I have receive 4 packages and wrote on the packages cancel and return to sender.  I am being charged for these $2 bills even though I send them back.  I sent them an email I think and informed them to quit sending these to me or I will have to take other steps to correct this.  Please let me know what I can do.