I would only expect to see a change in your external IP address when your hub drops internet connection and then reconnects have you checked the logs to see how often you are dropping internet connection?
it is quite normal to get same external IP address with very short disconnect/reconnet but your external IP will only change when there is a drop in internet connection so you need to check router internet connection time not router uptime
If there is noise on the line, then you need to report it as a noisy line. Do not mention the broadband problem, otherwise it will end up in the wrong fault queue, and take much longer to be fixed. There are plenty of people who can fix phone faults, but not as many broadband people.
Once the phone fault is fixed, then the broadband will get better.
The line test would not normally detect this, it need a full check of all connections.
Request another visit, if its not resolved after that visit, then a moderator can be asked to follow it up.
There is probably a bad connection somewhere. This is normally an issue if you are fed from a pole, as there are a number of possible failure points there. Usually the only solution is to replace the dropwire, and re-terminate everything.
Its either the wind blowing the dropwire and causing a disconnection where it joins the house or the DP at the top of the pole, or water getting into the DP (distribution point).
Sometimes its not possible to see the actual fault, so its a case of replacing it.
If you cannot make any progress with this, a moderator can chase it up.