I have never had that happen but I have done the trial mags before and then sent the cancelled bill only to get several more before I either call or just ignore them...It costs them money and me money to have to keep sending cancelled bill or request for payment...if you don't pay after 1 maybe 2 bills then stop...But what you got is uncalled for...I might send back a letter stating that if they have a problelm not understanding cancel then you will let your lawyer handle the problem ...that will probably have them drop the matter....LOL