INCORRECT WATER BILLING

My name is Mavis,Staying at Unit B514.I have a problem with Alumni prepaids whom are taking water meter readings at our flat.I stayed there for 5 years and had no problem with my water account as i pay it every month.Yesterday the 10.04.2018 i received a letter stating that my water account is in arrears with R 1204.87. The average payment that i have been paying all this years is not more that R 400 now all of the sudden i have to pay R 1200? I called the company and spoke to Sandra,she cant give me straight answer as to what is going on with my account.In march my statement was R 253.54 and i paid R 155.00 on the 4th of April and R 100 on the 6th but only R 155 is reflecting on the statement. They better fix this issues because i cannot pay for what i don't know.Somewhere somehow there is a person who is not doing his/her job.