Broadband issue

My broadband has been horrific for months, had an engineer out who said it was fine, it's definitely not fine but what am I meant to say to an engineer who thinks their word is god?

I need someone who can actually help to come out and fix

This is gig1 service and it's all over the place

I always set up a BQM as I cannot trust virgin and their "there's no faults showing our end" 

 

 

[Mod - Title edited for clarity]