Unfortunately, this is what your average Three customer comes to expect sooner or later. I haven't even bothered to contact support myself as I know I'll be wrung out to dry with your typical "reboot your phone" or "turn off your mobile data for a few minutes and turn it back on".
When I first joined Three a few months ago, the network was under maintenance and I experienced 3G (H+) speeds of 20mbps down and around 2mbps up, plenty for my needs. However, after the maintenance concluded and the 3G network was presumably decommissioned in my rural area, the internet speed has been absolutely abysmal on 4G to the point where I've had to get a secondary SIM from VOXI to simply stay afloat as my download speeds barely reach past 1mbps and the upload speed test often fails because of how terrible it is.
Although Three was a good network a few years ago, I would advise against joining them today. If you can afford it, get yourself a SIM with an MVNO like Lyca or VOXI and just ride out the contract. It'll be way better than attempting to deal with what is essentially the worst network provider in everyone's area (which you think wouldn't be possible as I can see a massive cell tower in the distance from where I live but hey, Three is always filled with surprises!).
If your signal is horrible and you're a person who is claiming government benefits, raise a complaint with Ofcom or the body for communication ombudsman as they should get your case sorted in the long run.
