There is definitely a fault on the line possibly at the street cabinet or exchange. If you have a mobile with inclusive minutes call 03454541111 otherwise freephone 08001831234 the sales line and select option 4 then option 2 which will put you through to customer services and faults.
An engineer needs to come out and have a look at the line by the sound of it.
Welcome to the forums and thank you for your post. Sorry to hear you've been experiencing landline issues.
This definitely sounds like something we'll need an engineer to investigate for you. Just to check, have you tried another handset to ensure that this isn't the cause of the issue?
In order to schedule an engineer appointment, we'd need to clear account security. this isn't something we'd do on a public forum so I'll send you a private message. Please head to the purple envelope in the top right corner to respond.