iphone 4s stopped recieving voice mail notifications

i have an iphone 4s on orange (uk) until about a week abgo was working fine. until i was asked why i wasn't replying to my friends messages i didnt realise i was recieving voicemails & missed a weeks worth.
i get the banner to say i have a misssed call but not notification of a voicemail being left.
i checked my settings when ringnig voicemail & all alerts are turned on.
i used to get a text message to say i have a new voicemail now nothing.
any ideas what i can do next?

thanks