How many mistakes can the CSA make?

My story. The CSA are just a bunch of untrained TW*TS. My case so I was told with letters and phone calls September 2013. 9 weeks later I was told with a phone call, they made a mistake.

Now September 2014, I told again my case has ended. I had arrears from non payments last year, so I paid by card.

Today I received a call from the CSA tw*ts, they have made another mistake. I still have to pay £79. Another mistake, how many mistakes do they make to how many people. WHAT A LOAD OF TW*TS!