Dissapearing Airtime and Data

I really thought that this time I would be writing a compliment not complaint.<br> Can someone explain what happened to my Data and Airtime this weekend at first my Data finished and I dind not even get the sms that its been depleted instead it went ahead and chowed my airtime.even this morning bought airtime and data and within minutes of changing sim cards my Data and my Airtime was gone.<br> <br> What's going on.