It’s not clear from what you’ve said whether you are having problems with Wi-Fi stability or with the Digital Voice. (They are separate things. DV does not use Wi-Fi, although it can use DECT with cordless phones).
If it is the Wi-Fi, as imjolly says, you may have to reset the wireless name and password but if your equipment is connecting and then dropping it suggests that is not the problem. (It would not connect at all if it didn’t recognise the name and password).
If it is connecting to Wi-Fi but not remaining stable it suggests interference due to the channel in use having changed. Going into the wireless settings and experimenting with changing the channels may help. (Your other devices will adjust automatically, so you don’t need to touch them).
There have also been instances of the 5GHz preventing 2.4GHz devices connecting properly. Turning off the 5GHz until all the devices have connected and then turning it back on again usually fixes this.
If the problem is with DV, have you rebooted the hub? It doesn't seem to configure properly until it is rebooted (and the paperwork doesn't mention that anywhere).
