I need a paid up letter or my money back

Made arrangements of R1500 for my MTN account with them on the 11th of October 2024 which started deduction on the 25th of October until 25 September 2025. This arrangement was made in accordance to the full amount I owed at the time. They deducted according with the agreement until 25 September 2025 but now I'm receiving calls from HP attorneys claiming that I still owe R10000 for the same account I've paid for the whole year. And when I check my credit records it still shows that I owe MTN