Don't want new gym members and are happy for you to open a membership at their competitors rather

I dont understand this company it clearly doesn't want to increase its customer base or increase its revenue!

I am trying to start a gym membership at Virgin Active Morningside and cancel the gym contract I have at Planet fitness Fourways however I am being told I am being declined for a membership due to an account with an outstanding balance of +- R2000 from 11 years ago where I was not even the signed account holder, I was 17 at the time?? No debt collector or accounts department has contacted me in 11 years regarding this amount and they wouldn't because again I was not the account holder nor was I the signed payer of the account.

The accounts department says there was another account opened in 2013 with me as the signed account holder and that account is up to date.

I am currently at Planet fitness and my account is up to date with them, my credit record is 100% clean, how can you push an outstanding balance onto me if I never signed as the account holder and was 17 (under age) to do so at the time the account was made?

Please get someone with actual authority to get in touch with me regarding this, I can easily just stay with your competitor at Planet fitness and move to the Planet fitness in morningside because I'm sure they want to increase their revenue and customer base.

Again this makes no sense!