Account unfairly blacklisted

Hi..hellopeter..I am truly disgusted by how Gym company treat their members...I have long left their gym of which I don't understand why a person being charged if they had not attend gym...I'm pretty sure we all have an access through using our discs not fingerPrints which scales how many times a person have been to gym...I have just received a message that my account have been blacklisted..which I remember last year when I received their last call I then I asked them how does one owe gym when they're not attending at all...this will ruin my credit score and jeopardize my credit and put on my profile in bad books...help me out please