I also had phone line problems. First time I could connect to broadband, but there was no dial tone for narrowband or phone calls and second time everything went dead. Both happened after after heavy rain.
Start by looking in the Phone Book for advice (and perhaps diagrams) on checks to make at home. Then, if need be, go to BT's main website
http://www.bt.com/ and in the search box type 'report a fault'.
It is important to do all possible checks at home before asking for an engineer to call, or you could be faced with a hefty bill if it turns out to be something you could have discovered and dealt with yourself.