MTN Please TALK to your customers

I am using your excellent service as this is the only a customer gets to speak to MTN. I have been with MTN for 23 years and the only way to get a result is this. For the last six years I have had a modem and 5g contract with them. My averabg use was about 5GB a month. Over the years i built up a carry over which eventually grew until aai built up a %gb carry over every month ie I started the month with 10GB. In september I had the buy a gig to finish the month. In October I had to buy 10GB extra to get through the month and I have now used 7GB for this moth already. I have phoned them, I have been in store and I have interacted with MTN Active. All I want to know why I am suddenly using double my normal data. I closed on account in October and the other three expire in february. Will MTN please explain or do I go against my heart and change service provider.I dont want to leave NTN but I will if dont get an explanation I will go.