When listening to ‘ringtone’ on the calling phone ( mobile or landline ) with the destination phone not ‘ringing’ , ask for the phone handset to be picked up ( as if the called party had heard it ‘ringing’,and answers ) if the ‘ringtone’ trips and a conversation can be held , then the ‘fault’ is quite a common one, basically the exchange isn’t sending ringing current to make the phone ‘ring’ , but the exchange is effectively sending ‘ringtone’ to the calling party.
If the call does connect , the person who has the non ringing phone , needs to report the issue to their provider as ‘BNR’ , which is ‘bell not ringing’ , obviously before reporting it, the phone instrument itself needs to be checked in case the ringer is turned off or the phone is faulty, this can be proved by trying the suspect phone somewhere else, or by swapping for a known working phone, however this would explain if other people can get through OK and it’s only you that has an issue
