What sort of 'fibre' broadband do you have, if it's FTTC ( fibre to the cabinet ) have you done any checks to verify the phoneline the broadband runs on, is OK ?....you need to try a known working ( preferably corded) landline phone in the master socket test port , if no dialtone in the test port , then your line is faulty and should be reported as faulty , NDT .
TBH, it's more likely that your individual line has an issue rather than a major fault affecting many other customers as well as you...if there is a major fault they probably would advise you of this when you call to report your individual line.
If you are FTTP, then the checks required will be different
as @iniltous said is your phone line working and if so is thete any line noise?
it is an essential piece of kit and for investmemt of about £5 for a cheap corded phone could save you engineer callout of £85