In reply to The Potato:
you could try a new filter, they are super cheap.
Two other things I can think of are try manually changing the band your wifi uses instead of it being automatic, second one is order a different brand of dect phone online to see if it solves the issue, if it doesn’t send it back! I guess last resort is a new router.
if your wifi router is freebie, buying a good one wouldn’t be a bad thing anyway, I recently tried a brand new bt smart hub and it wasn’t a patch on my 6+ year old tp link router I bought for 100 quid.
Post edited at 06:56