Fault not repaired

We as a company has experienced the past 12 months such bad performance and assistance from Telkom. We have 8 incoming lines to our switch board. We have reported a problem that when we receive a call (1 in 5), the phone rings, we pick it up, nothing on the other side, switch board shows message "hang up", 3 times in a row. On the 4th call the person who called eventually get through. We have had many clients informing us that they cannot get through or that the phone only rings. How many clients do we have to loose before we get any help from Telkom?