Billed for services not received

On the 6 Feb 2015 I was billed for R150 for a code U770731. I never asked for this or received it. I phoned on the 10 Feb 2015 as soon as I noticed it on my statement. I was given a ref number S3-8W123-3NSSU and assured they would sort the problem out. I have since phoned on the 18 Feb 2015, 24 Feb 2015, 27 Feb 2015, 4 March 2015. On the 6 March 2015 I went in to Nelspruit Vodacom and they phoned and was assured it would be sorted out. The lady spoke to me again on the 10 and 12 March 2015. Since then I have heard nothing. I tried to sort it out again on the 27 March 2015. I am getting no where and in the mean time they have taken the R150 out of my account. I am told it was for an upgrade which I was not due for and never received. I did upgrade on the 24 Feb 2015 at the local Barberton branch where I paid them for my upgrade fee. I am now at wits end and need to take this further.