Its a tough call here, I can get speeds up to 16M on the 3 IP Pro plan often but then every few months it slows right down like currently until I call in and ask them to check my line. They go and check and come back and say, "no, everything looks fine here", then I go run another test and my speed is back up over 13M almost guaranteed so I'm starting to think some monkey business is creeping into their game now. I was losing service all the time with my phone or one or two of my IPs, they have promised credits and never came through with them but they never miss nabbing me if I go over a few Gigabytes now and then.
That sounds like a billing issue, so why not follow up with the billing department and reference that tech you spoke with.
Have you tried creating a thread to obtain support for your issue? If you provide your MAC address to a Cogeco employee, they can look into it and publicly explain the issue so there's no possibility of any 'monkey business'. Give it a shot!