Gym with hidden stipulation on contract

I have a 2year contract with the gym when I joined it was my self my wife and my gym partner. We joined the gym mid month and they told us that we can train for free and only pay the month end for the new month I then paid up front for the next month. The gym then went and made a deduction on my account after I paid up front for the 3 of us they then told us the head office said we must pay and advance for the days we are training that was so called for free. In the contract they want a leavy fee at the 6th Mont of the year my deduction goes of the 1st of every month only the monthly fee went of on the 5th of the month a leavy fee went off and the stop order was returned by the bank as I did not have the total they wanted to deduct in my account. The same nite I went to the gym and paid the leavy cash. I was then told that all 3 off us must pay a bank return fee for the debt order that was return. I told them that they are at fault and that the debt order was supposed to go of on the 1st and that I paid it cash. The lady helping me informed me that the head office said that all 3 of us must pay for the 60 rand debt return. This I can't under stand as I am the 1 who has to pay bank fees for the return band deduction and this after the payment was made cash to them on the same day. Refusal of us pay places us on brich of contract and no entry into the gym.