Unauthorized debit date

I joined the gym in April/may, I have had 3 unauthorized debits occur on my account. I advised that they should debit me on the 2nd of each month, however they have debited me on the 25th, 22nd and the 15th. I have reported this to Martin, the gym manager, several times with no assistance. Last month I called Martin, he said I should report it if I want to. This morning I was debited again, I called him and he said I should report to their accounts department. Gym company doesn't even have a complaints line. I need your urgent assistance. The debit order even bounced previously and I had to pay the bank for a debit order I hadn't catered for.