Packet Switched Data

Hi<br> I`ve got an 2gig MTN contract. It`s my third year into it. I have been paying an average of R105.00 each month. Each month I receive 2gig. I only ran out of data once and when I did, I purchased data online. This happened in August. September I received a bill of R1718.80. The first time in three years. A total of R1947.80 was deducted.<br> On 11th September I received a SMS on my Cell stating that I have exceeded 90% 25 of my credit limit of R1826.00. I didnt and still dont make sence of this message. I went in-store to query it. I even went to a major MTN service centre. Both give different explanations for this message. I even called MTN customer service but even they weren't helpful.<br> One thing that I was told is that I have an OPEN contract. I dispute this. My contract doesnt state this. I only receive 2gig. My bill states that I incurred Packet Switched Data Calls charges. I want to know what this is and how and when I incurred it. My request up till today was not fulfilled by MTN. For the last few months, I get voice messages saying that I have insufficient airtime to make calls.When I check my balance, it shows otherwise. Immediately afterwards I can make calls.