@OP did you try calling support to report the problem? It's almost impossible to diagnose ANY internet problems (not related to your own equipment of course) and the ISP has tools and access to do it. In any case, it's much easier and faster to contact support.

In my experience, even if I discover what is the problem, if it's on their side I still have to go through support to get it fixed, so I just wasted my time. And in most cases the lowest level of support doesn't even write down the information I give in the ticket, even if I send an email.