When your phone only rings once then cuts out, this fault is known as "ring trip". It can be caused by a number of things either inside or outside your property, and will require a process of elimination to track down the cause of the fault.
Techjunkie.com One sign that your phone calls are being ignored is how many rings before it goes to voicemail. Generally, the feedback ringtone will go through several cycles before the voicemail message comes up. If upon placing the phone call, it rings only once or twice and goes to voicemail then your calls are probably being declined. 443 is also the number to dial to retrieve voicemails. To switch voicemail off dial 1626. Voicemail deducts one minute from your Goodybag regardless of length of call (assuming you have minutes left) or, if not, costs 8p per call.

With voicemail all set up, you can now access and listen to your messages. In the Phone app next to the Voicemail tab, you’ll see a badge with a number, which represents the unheard messages you have. To listen to your messages, open Phone app and tap Voicemail at the lower right side of the screen.
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