Not hassle, just facts of the job..
or do you expect life to be perfect?
Just about everyone has to pay the install charge, they've bent over backwards to free up a line for you and now you have a secondary fault over a month later and not associated with the initial install. Also the fault described sounds like it's intermitant and probably a pain to track down, yet you moan at the length of time it takes for an engineer to come. If you wanted a 6 hour response time then pay the extra and get a business line..
Yes a fully working phone line would be great but give the guys a chance, they are only human with restricted time to get round all the calls