Threats of being Blacklisted

I joined Carlton Gym which now falls under Gym Company and for years I kept paying for a service that I didn't even use (I still am paying for this). I then lost my job and missed about 3 payments due to this and I'm constantly getting messages that I am due to be blacklisted. When I got a new job they continued taking money from my account yet every month i'm being told that I will be blacklisted.. (I'm guessing it's for the three months i had missed)...how is it them my fault that when they started debiting from my account again they didn't take money for that missed 3 months? I'm annoyed and highly upset.