Unacceptable amount of disconnecting and bad connection

For months now, my connection is constantly dropping or is very spotty and my upload speed, which I need, has become none existent. 

I've already has 2 engineer visits out, one who didn't even know how to work his own pad and another coming this Saturday, each time they say they can't find a fault in the house or the street and it's definitely not my PC, as it happens on every device.

I work from home, so I need it fixed or it may be time to switch ISP.