Connection drops to little or Zero speeds until I Unplug router

So I've been with VM for about 16 years at my current address and up until 12 months ago had pretty good BB service, always had the highest speed they offer and been happy with it.

In the last 6 months I've had 6 or 7 engineers attend my property I've had 2 new routers, the cable pulled from the cab and replaced, accentuators fitted and removed and yet another new router this morning and I'm still facing an issue where at random times through the day my 1gig BB drops to 1mb or less, until I unplug my router and plug it back in and after about 2 or 3 mins it reboots and its fine again but I've having to do this up to 6 or 7 times a day. 

Again an engineer attended this morning, new router new accentuator fitted as the power was to high at 13-14 and needs to be lower but just now again same issue huge speed drop, cant even load a webpage until I reboot the router and yet again Virgins answer is to send me another engineer again tomorrow the I've got to wait in for. 

Has anybody else had similar issues? Any advice? Thanks