BT / Sky Broadband.
I built a new house, had a phone line put in with BT and then took Sky Broadband.
Anyway, it was apparent there was a problem as the modem would lose sync for 5-10 minutes randomly. Tried several routers and eventually called them as I couldn't fix it my end.
They were pretty good in handling my problem and booked a BT engineer visit within a few days.
Sods law.. He comes out and "finds no problem", and says that I "may be charged a call out fee". Thankfully I wasn't as Sky could see the disconnects on the line. Their solution was to slow the line sync down to increase stability.. At which point I decline due to it being a new line and new house.
Anyway, after several calls (I'd guess 10) they agree to send another BT engineer.
Thankfully, the guy that came out is a friend. He checked some basic things, and by sheer luck "hears a noise" on the line and it's coming from the pole. Great! He tells me that the brass screw terminal on the pole is causing problems so crimps my line in a way that bypasses the pole.
Anyway, the line got better for a week then I'd get problems at specific times and knock out my service. This time I record the times and start becoming obsessed with fixing it. Turns out it is a REIN issue caused by electrical interference.
Ok, so call up sky and explain that I think I know what the problem is.. I get passed to the technical team and he is impressed with the info I give him and agrees to book a specialist Internet engineer (lol) to come out.
BT man arrives and says there's no problem but he agrees that it is likely a REIN issue, but he cannot do anything about it as he's not qualified FFS
I start Googling on how to detect, pinpoint and eliminate the issue which leads me to dig up good info. I call back the engineer I know and he comes out. We wander the neighbourhood with a portable radio and by sheer luck we find a possible source.
He gives me some info and tells me that only Sky can request the REIN specialist visit, as there's only 1 in the area and so I call Sky.. Cue explaining the story AGAIN and them asking if I'd like a reduction in speed etc at which point I said "send the engineer out.. I'll explain to him if it's easier".
They send another chap out and although it's not the REIN specialist he does know the chap and agrees to rings him. We arrange a visit that weekend as I've already taken 4. Or 5 days off work to sort it.
I'm in work one day, and my wife calls to say "the BT man is here".. I speak to him and he says he can't find anything at the time, but he will swing by one night after work and come back when it's regularly been happening..
At this point I get the electric company involved and they are amazing.. They come out and check all the lines in the area and really go all out, but the issue lies with pinpointing the source so BT need to do that.
Anyway, after a week BT never arrived and im still waiting! It's been about a yeart and although I know where it is, getting someone to come out and witness the problem got the better of me.
I was fortunate that the local village had wireless broadband installed, so I cancelled the line and told BT to do one. I even emailed their CEO and got a decent response but never actually anything that was close to a solution.