1.2gb wifi regularly dropping to around 30mpbs until its reset.

As above every night for the last few weeks my WiFi has had issues, it has regularly dropped to a sub 30mpbs speed and the signal in my office on the other side of the house is awful now regardless, ive even bought a AX1800 wifi usb wifi adapter and attached it to a 8m usb lead so it's sitting in the hallway and I cant get above 100mbps at the best of times, the rest or the time my signal is non existent. Ive been trying over the last couple nights to contact virgin media but after ringing 03454541111 and going through about 5 minutes of automated messages the option to get help with broadband just ends the call. This has happened every time ive tried (around 10 attempts) I hear there is a way to get an engineer to come out with an extension cable to move the hub to a more convenient location. Is that another number? 

Thanks in advance