Outrageous municipality bill

I'm very disgusted with city of tshwane and my electricity bill,according to them I owe them R20 000 from 2018 but I paid them R10 000 already which they said does not account or balance the outstanding R20 000,I've been to their offices but no one wants to help me in resolving this issue,I'm out of ideas as to how I can receive immediate help,I'm a pensioner and I live with my disabled son yet I have this issue to deal with, which very stressing and financially I'm unable to pay off the money,I have been paying every month but the statements reads owe them. Pretoria west/Danville