I bought a second contract with MTN but instead of deducting a debit of R1300 we agreed upon they deducted R4300 as from February up to April (3 months) that I do not know

I bought a second contract with MTN but instead of deducting a debit of R1300 we agreed upon they deducted R4300 as from February up to April (3 months) that I do not know. Pls intervene I need my money back.