Contract not upheld

I recently upgrade my data contract to 400g anytime and 400g night . This was effective in early December 2022. I received this amount of data for December and Jan 2023 and then in February 2023 the amount of data received was 250G anytime and 250G night time. This reduction in data took place without explanation and to the point that I am out of data. I have to contact Mtn several times in the past 2 days and and go into a branch The problem remains unresolved!!!