Incorrect Debit Order Amount

I have always wanted to join the gym especially Virgin active over the years but was sceptical as a lot of people always complain about being incorrectly debited by the gym and always a HIGHER amount never a lower amount which seems to fishy to me. I do not think its a mistake I just think these are just a bunch of ******* ******. I took up a membership in November last year and for the 1st month the debit order was correct now all over sudden the amount that I was debitted for in January is higher. I need someone to urgently contact to rectify this error or else I will reverse this debit order and cancel this membership. We have a contract in place where I use your facilities for a specific amount, you have already in the second month breached the contract and I have every right to cancel it due to this. SORT THIS OUT, I AM GIVING YOU TWO DAYS OTHERWISE I WILL TAKE THE MATTER FURTHER AND CANCEL THIS CONTRACT