Fortitude Crossfit

Review: have attempted to cancel this acct. since july 26,2014. I keep receiving bills in the mail. cancelled the automatic withdrawal from my checking acct., spoke with and sent letter of cancellation with the owner "[redacted]" and still cont. to receive bills in the mail. also have sent 2 cert. letters in regards to this, one to member solutions and one to [redacted] at an address he states is for Fortitude Fitness. I don't know what else to do concerning this matter. today I received another bill from Member Solutions p.o. box 297, Hatboro, PA 19040 (this is were the bills come from) and threatening to ruin my credit if I don't pay. Also attempted to settle this by phone with member solutions ,but no manager is available when you call and they say they will call you back and they don't. I have excellent credit and afraid this might hurt it, but I don't know what else to do. the actual name of this business I signed under was fortitude crossfit, but the bill comes from member solutions and states on the bill that "account for service is under Pinnacle Fitness of Slidell". I only have the owners phone number who I have contacted several times via text and in person. there is no actual phone number for Fortitude crossfit or Pinnacle Fitness of Slidell.Desired Settlement: I want this membership terminated and don't want to receive any more bills from these people. Im now worried about them ruining my credit.