Not allowed in the gym even though it is paid for the year

I’m giving a star because there isn’t an option for no star. I paid for my 3 children and full year membership and they called me many times to tell me that the accounts were in arrears. I explained that I paid one year and sent the proof of payment more than 3 times already and got mad at one of the consultants. Now my kids go to the gym and they aren’t allowed because according to them no payment was made, my children called to explain that and I asked to speak to the person who didn’t let them in, very arrogant lady who tells me that for my kids to get in I have to pay, if I can’t benefit from the gym if I don’t pay, I explained that I paid and one more sent the proof of payment to my son to show to her and she then tells me that I paid for the whole year and should have paid every month and for that reason it counts as not paid and I should resolve it with the main office.