Changes in price plan due restarting of mtn app

I recently brought data using my own bank account on the 15th of December 2023, on the 25 I realize that data had depleted day and night data. Called the call center told I had changed price plan and lost all my data and airtime. Funny the airtime is still there. Other consultant told me that mtn is moving customers to the Mtn bonus bonanza. How can I be stupid to change plan when I still had a lot of data thar expires next year on the 15th? I have been given emailing customer@mtn, calling in hoping I'll get someone experienced to give me my data back. Not rude consultants who tell me I lost and there nothing they can do. The changes happened when the mtn app wanted information from me as if it was my first time downloading it