voluntary limit of R300 exceeded

Up until the morning of 28/12/2015 I had a voluntary call limit of R299<br> On the 27/12/2015 this limit was reached.<br> I contacted the call centre, and asked them to increase this by R50. <br> <br> I am now being slapped with a bill for R1500+<br> The monthly contract cost is R260. Plus a voluntary limit of R349 as of the morning of the 28th (which I specifically stated over the phone) plus a R29 data bundle.<br> <br> Charging me more than this is a breach of contract.<br> <br> Where in hell did this bill come from. I cannot and will not be held liable for a failure of Vodacom systems. This billing figure will be reversed or my legal advisor will be contacted.