Didn't receive monthly airtime

<p>Hi! I hope you can help me. I've written to MTN a few times last week but haven't received an answer yet. I am supposed to get R110 worth of airtime every month. On 21 Dec. I received the customary sms informing me that my account has been credited (I pay via debit order on the 15th), but the money wasn't added. The 25 free sms's were though. It almost looks as if R110 was deducted instead of added, because I regularly check my balance and since I don't use my phone very often, I can't see how I could have lost about R100 in a couply of days, instead of receiving R110. My balance should be over R400, it's about R230. My account is A ********** and my number is ********** 077.</p>