Good day Sir or Madam

I am a Zone fitness member.
I went to the branch and handed the receptionist my change of banking details. She never informed me my dad the account holder of bank account has to hand it in himself.
She took it and said yes it is in order.
They blocked the hymn account as debit was not done by Zone Fitness on new account.
I went to the branch paid in the money in cash and told them again to change details to new account.
I was not allowed to make use of the membership.
They handed the account to there lawyers for the amount of R8000.
I went to the branch Samantha the manager said is not there fault I am liable to either pay the Lawyers amount or the amount of R3500 at the gym in full and I am not allowed to do it in two payments they are not going to accept two payments.
She also told me they will add an amount of R350 every month.
Please advise me on the complaint.

Regards
Tyshae Mehl