My account was debited for more than I had availab

I had purchased some products over the Internet and it cost R452, I new I had R900 available but the company I had purchased from debited me for 4 times the amount, I had lodged a dispute with absa card but I have not received any reply as yet. Why would absa allow for a foreign transaction to go through my account if I did not have the funds. I would have expected a call to confirm the transaction. I have made 7 calls to absa but no one can advise me what is happening.