Bad Channel Bonding on several channels. Please help.

I can almost never get 50mbs download speeds even though I pay for it. I have been dealing with this issue just over two years and had two technicians out to try to resolve the issue with no luck. The first technician replaced every connectors from the box in the street to the modem, but still had issues. He then installed an amp to get the signal where they needed to be. It appear to help, but I am still getting errors logged by the modem and I cannot get 50mbs download. Most of the time it is somewhere around 15-25mbs.  The technician said that there was some type of noise spikes coming from the street so he put in a ticket to have a street sweep, wherever that is, done, but it has been over a month and I still have issues. I had a second technician come out, but he seem to think the problem was that my virus scan was running. He turned it off and logged into his special web link and it appears to get 50mbs, but as soon as he left I tried and could only get 25mps. Anyway, I still think the noise issue from the street need to be resolved, but when I call COX they tell me they cannot see in their computer the tickets. They seem to indicate that some other group handles these and they have no idea.