Ringtone length

My phone used to ring for 30 secs before going to voicemail. It now rings for 15seccs 0nly without any request from me, Far too short. I eventually was able to get help via the chat system and was given the number to ring to change it .This I did and was told my request had been registered. But  when tested only 15 secs of ringtone occurs. The helper was puzzled and could only suggest that I disabled 'voicemail" to solve it . This seems drastic and I don't want to do that..

Any suggestions?