Incorrect handed over account

I am so highly irritated with Zone Fitness, they submitted my account with them to nimble group for arrears when my contract is up-to-date as they are deducting monthly from my bank account. I have reported this since last year and this year I am receiving daily calls from Nimble. they told me their head office has dealt with it and informed nimble this was an incorrect submission. Clearly this is not the case as I am still receiving calls daily from nimble and I feel zone fitness is messing with my credit score.