Broken ADSL

The internet light on my modem suddenly started flashing and we experienced an intermittent internet connection. I called the call Centre who eventually advised that we replace the modem. A new modem was installed but the problem continued. Thereafter I went on to log a fault about 3 times. Each time I was smsed that the problem was fixed when it was not. Yesterday the problem seemed to be getting worse and we could not connect at all until 10pm where it suddenly started to work. Today a technician came out and told me the problem was that Telkom sold us a 10meg line when the infrastructure can only handle 4megs. He left saying everything else was fine and that we should just change the plan. I called the call Centre and did so. I then called tech support to find out why the connection got worse. I called three times, only to be practically screamed at and told that the technician will come out to see me. This does not make sense because my internet used to work fine. I don't understand how this is an acceptable explanation.