Incorrect municipality bills

I bought a gouse un 2014 in Duvha Park extension 9, I have been paying my municipality bills monthly without missing a payment. I have been paying the amounts displayed on the statements. Since July 2017, I have been getting bills that are 3 times higher than what I was normally paying; I kept paying but now I'm surprised that the municipality says I owe them R9625.21. I dont know how I can owe them this amount when I pay my municipality bills monthly. I have complained at the municipality and I was told to write a letter and I did but they never gave me a response. I complained to them again and they said they will send someone to read the meter but they never did. I'm very frustrated and I now realize the municipality is robbing me and they can't explain any of these charges they say I owe them. Please help.