Bad service

I have a data contract with Mtn and I signed a contract of 300gb (150 day and 150 night) but for the past 4 months every month on the 9th it says I no longer have data no matter how many gb I had the previous night . I have been complaining and no one is willing to assist me. And when I check on the app how many gb I have used for the past 30days it doesn’t reach the gb I signed for. Can you kindly assist please because I cannot pay for something am not satisfied with