@Angry8 welcome to the forums.
Wi-Fi issues can't generally be fixed by PlusNet staff, they can make suggestions to try and improve things. Wi-Fi is basically outside their control - I avoid Wi-Fi as much as possible and use wired connections. Their are simply too many Wi-Fi devices around fighting over the limited bandwidth available. either from within your property or from neighbours.
Take a look at: https://www.plus.net/help/broadband/getting-the-best-wifi-signal/ and
You could also logging on to your router and splitting the 2.4 Ghz and 5 Ghz bands so they are not being used as a pair. This has been known to help in some cases.