I’m surprised it’s so low. Ought to look into the line stats and consider the usual measures for improving connection speed - different modem, cleaning up wiring cleaning, up path into the house, getting rid of all extensions.
I would not give up hope. If it worked before then it will most likely work again as there’s probably just a fault; the other possibility is there is a new huge source of noise in which case unfortunately you are screwed.
I strongly recommend you talk to Andrews and Arnold who have a "fix your line or your money back" offer, where they will actually take on other isp’s Faults and beat BT up if they can, to get it sorted. They are not the cheapest ISP but they are one of the very best; They are not cheap because (i) they employ only very clued up people not chimpanzees on the phone trying to read scripts and (ii) they don’t overload their network so they have to invest to keep improving it as usage rises all the time.
A&A can’t always win against BT who can turn truly nasty and they have to be careful but they always do their best.
The alternative is to go to 4G. Definitely worth considering if the signal strength is adequate, if the cell is not overloaded with traffic and as long as the basestation is not going down all the time. Some seem to suffer from outages for reasons unknown.
In fact A&A can help you to go to a mixture of DSL and 4G combined.
If you don’t go for 4G and you have deep pockets then some other ideas. You could order a new line and see what that’s like, then cancel the old one. If you want more speed then as I suggested you could consider combining 4G and DSL but you can also (again deep pockets) get double speed from using two phone lines ‘bonded’ together by AA.
I have four DSL lines bonded together and that gives me 9.8 Mbps downstream 1.3 Mbps upstream (TCP payload; figures from several speed testers). I wanted a lot more speed and vastly better reliability, and in fact the combined link has not gone down in nine years, 100% uptime, because if one line goes down then this is detected and traffic is just diverted to the other lines. I also have automatic switchover to 3G as extra backup now. (I haven’t got 4G hardware set up yet, although I do have 4G service available as well as 3G)