BILLING FOR INTERNATIONAL ROAMING

I was charged for international roaming last year in July and have trying to sort this issue out since then. I did not make or receive calls however was charged for calls. When I queried this Vodacom said the calls when to voicemail and hence the charge. I have not had voice mail on my cell since August 2010, the date was verified by Vodacom in Nicolway. I have requested proof of these calls and have received nothing. This is now going on for 10 months. I would like the full amount plus interest to be paid back, and I will definitely change service provider when my 3 contracts come to an end. The reference number with Vodacom is S3-8XW8T-TZ49.