Incorrect debit order

In 2018 I signed a Sim only 24 months contract. I upgraded during the 23rd month in 2020 before expiring. And in 2022 during the 23rd month I upgraded again but the debit order was R1200 instead of R339. I called their call center but they can not explain what the R1200 is for. This matter has not been attended. No investigation was conducted regarding this matter as promised.