Packet switched data calls

Dear MTN<br> I HAVE A 5G data contract on an Ipad and the data is shared with my handset on which I have a 500mb data bundle. I have a very average data usage. However on my 20/12/2015 invoice On my handset no *** I was billed for R454.17 and my 20/01/2016 invoice shows R458.01 for PSD calls. I have never incurred this in all the years I have been with MTN<br> I check my data usage at least once a day, and have had carry over data every month. My Ipad no is ***<br> I have made numerous calls to 808 and I have all the reference nnumbers. I have also sent a few e mails.<br> I am always told to wait 4-10 days for a response. Which I never get!<br> Please advise me on how to fix this problem. Annette van der merwe