outstanding debit authorisations

On the 25th September I made an online transaction. On the merchant website, my request failed but the amount of R1490 was subsequently deducted from my account. The amount does not reflect on my statements so I'm stuck in a loop where the merchant is telling me to contact the bank and the bank is telling me to ask the merchant to authorize the request. I cant fill out the dispute form as I don,t have a decline slip since it was an online transaction. I therefore have to reverse the transaction for a ridiculous fee of over R300. I find it really odd that it could be so difficult to cancel a transaction for money that technically hasn't even left my account