iphone 7 red dot notification

Hi folks,

New iphone 7, got a 32gb then swapped it to 128gb. Not sure when it started but i get a voicemail notication red dot on the vm call button inside phone app but noton home screen and also there is no number dispalyed. It diasppears when i call vm but then comes back randomly, any suggestions as to cause and soultion please?

many thanks T222