Unauthorized debit order

I took out a contract online around January, the package was SMART XS+, which is R125 per month. Last month R580 was debited. This month R380 was debited, WHY??? I WANT TO KNOW THAT WAS AMOUNT WAS DEBITED INSTEAD OF R125 THAT I AGREED? Surely my telephone conversation was recorded. Also- i got 2 sim cards , which i was told the other one was for free data that came with the offer- the initial offer was 10 gig but i got 6 or 7 gig, and the following month got data which for me i thought it was what was due to me since i didn't get all the 10 gig. Another thing i cant use the phone- whole of last month i didnt used it-it was off because the battery dies within hours of charging it. What must i do with the handset that i cant use?