In the UK we are lucky to have a bit better of the system - Openreach (or Virgin) own the cables, and ISPs pay Openreach to do the transit. IP based not dark fibre unfortunately.
That said, most ISPs won’t escalate when there’s an OR problem, or at least take a long time to, and then the OR tech is usually just trained to test the cable coming in and not a lot else.
I used to be with Andrew’s and Arnold (run by @revk who surfaces around these parts sometimes!) who were fantastic, because while expensive, the first person who answered the phone understood your summary, trusted you, and would happily beat up OR on your behalf.
In the context of UK infrastructure, "OR" is an abbreviation of "Openreach", part of the BT Group that is responsible for the infrastructure from ducts and poles to street cabinets and exchange buildings. It is not an organisation that an end user can access for support and is charged by ISPs to repair, upgrade and install additions to large parts the telecommunications network. It can be difficult to convince one's ISP to have Openreach investigate a physical fault or bottleneck, unless that ISP is the aforementioned Andrews and Arnold who literally implemented automated methods to repeatedly bounce faults back to Openreach when the latter insists on erroneously rejecting faults. Makes for entertaining reading :-)
That said, most ISPs won’t escalate when there’s an OR problem, or at least take a long time to, and then the OR tech is usually just trained to test the cable coming in and not a lot else.
I used to be with Andrew’s and Arnold (run by @revk who surfaces around these parts sometimes!) who were fantastic, because while expensive, the first person who answered the phone understood your summary, trusted you, and would happily beat up OR on your behalf.