@Dorsetroyal You should of asked where would be best place to have it in order for my PC and TV device to get the best speed. Instead they followed your instructions, which wasn't the best place to have it.
You now have several choices, either to get a new router your self and install that yourself or get in an electrician who can install a wired cable to the other room, should easily be able to do it without it looking unsightly.
As already pointed out , changing from ADSL/VDSL ( FTTC ) to FTTP can’t really have anything do with your WiFi problem , if your new FTTP router is located in the same place as the previous router and nothing else has changed either , then suspicion must be with the router itself , either by being faulty , or being ‘setup’ poorly for the environment in which it’s being used , I would have pointed the finger at the new router being faulty , but apparently a different router has been tried.
Your issue illustrates the problem with WiFi , no ISP will guarantee speeds apart from at the hub even with wired devices it has to capable of using the speeds the hub is delivering ( some posts about poor wired speeds turn out to be the device not being Gb capable )
The OP hasn’t stated that the speeds they pay for are not available, ( with a hard wired device ) just that the WiFi performance is not what they expect, given that there was no real WiFi problem with their previous FTTC service….it’s not the same issue as yours at all
When you installed the new hub did you go round changing all the WiFi devices for the new hub SSID and password and. making sure they connected or did you simply change the new hub SSID and password to that of your previous hub and that way the devices would connect automatically without a problem?
The OP case is totally different , closing a fault report of ‘low speed’ when there isn’t a fault with speed at the router ( the point at which the speed guarantees ends ) seems totally reasonable, the OP’s WiFi performance is curious , but explicitly not covered by any speed guarantee as there are far too many environmental variables, given that the previous FTTC service apparently worked satisfactorily, ( obviously only up-to whatever speed the FTTC delivered , so absolutely less than 80Mb ) if the hub hadn’t already been changed this would have been the obvious suspect, and personally I would be requesting a third change out of the hub ( unlikely as it may be that the two previous hubs had the same issue ) but it seems to me the OP ‘complaint’ is who should be responsible for the costs of providing the WiFi extending equipment and nothing to do with faults being inappropriately closed as ‘fixed’…as far as why the WiFi is so much worse now that previously, it’s a puzzle, perhaps some external ‘interference’ has coincidentally appeared at the same time …possibly a neighbour also changing a router and their ‘ new’ service causing interference