Finance department cannot add or count

Absolutely disgusted with VA. My son canceled his gym membership and requested it to be frozen (he has just finished matric) it is my responsibility to now pay R3000+ I agreed to pay it off as it's a huge amount to pay yet they phone me daily. I asked to pay it off but everytime I have paid an amount it suddenly increases and is now o wr R3900? How on earth is this even possible? I understand the cancelation fee but it can't accumulate and incr3ase when it's being paid off. Something funny is going g on in the finance department, *******ion? *****? Who knows in South Africa