Airtime always gets missing MTN taking my airtime for no reason

MTN I have a problem with you, each and every month I recharge my small phone with 5.00 rand I use this to open the gate in my complex, but my airtime every month it disappear always after a month and to me this is wrong. You have to stop this and pay back my airtime that you have used. This phone is not having internet don't even go to internet issues, its you MTN. Stop this nonsense and pay back my airtime. My MTN # is ********** 241