Tfg keeps on increasing my debt when I make payments on time each month.

I'm lodging a complaint on the insane increase on my tfg account. I'm a student and recently rekindled my tfg account because I needed some shoes. I have been paying off my account on time each month since I took the shoes, but the amount keeps on increasing without me noticing snd having no single clue why it increases.Last month I had a balance of R1266 but today upon making payments came to find my balance is now R1356. Tfg what kind of bad customer service schemes are running?