Voicemail says it's full when I only have a few messages

I have a 5S iPhone. Friends have told me the voicemail is full. But I have deleted all but 5 messages. None are over 2 min. I took it to an "IRepair" place, but he couldn't fix it. Said I should call Verizon to reset voicemail. I have tried to "reset" my phone by turning off and then on again. Nothing has worked.