Overbilling of accounts

I have been a loyal customer to Telkom for about 7 years now. After I missed a payment previously, they took it to collections and collected within a couple of days and charged the R200 however this time they did not come back to collect the money but stated that they were working on the case, however subsequently invoiced double the amount 2 weeks later. The customer service line doesn't actually take you through to the billing department, I have tried countless times. When you call the store they refer to the same useless 081180 number which results in no assistance.