Airtime bad customer service

MTN... REF: ********** 10 spoke to primose at 16:10 on the 19th feb .. with regards to my airtime thats disappeared from my line .. im on a R110 on a monthly basis and was told I cannot have more than 650 rand airtime on the 13th Feb 2018 I had R435 airtime and then on the 14th when I got my new allocation I then only had R250 that makes no sense to I then called in to call centre and went to the storelogged a complain and they come back with resolution ... dont know what happend... how can a service provider do that... I want whats owed to and please I want a call back on ********** 572 reduwaan