Pathetic service/ *****/ no problem solving skills

Very long story short.... have an account with planet fitness for 2 and a half years now. Someone else used the account (all my details just their banking details) after a year or so I decided that I will go back because the account is still on my name. I then cancelled the blacktag and changed the debit order banking details (filled in form) banking details were never changed now they want to hold me responsible for the outstanding amount, but blacktag was cancelled. When this all happend I went to the branch stood next to the Branch Manager and she changed it on the system from the old banking details back to mine.this all happend approximately 3 weeks after I filled in the form. Still not sorted out and going for 4 months now. Absolutely pathetic... I almost asked them on a weekly basis. They kept on saying they will follow up. On phone calls the lady said to me maybe the forms got lost somewhere between them and the office- when I requested for that they can't get the particular voice recording... all of this fuss just because one person could not do their job... Left my tag there. I will go to a place where they will make it a priority and have problem solving skills