A Merchant has more control over a clients account

Good day<br> I made an internet purchase yesterday afternoon. The product was advertised for R395 but when the transactions was processed two amounts was deducted from my checque account, totalling to over R3000.00.<br> I immediately made contact with Standard Bank. Nelly confirmed @ 10:00 that she's not in a position to cancel/reverse the transaction as it takes 24 hours to reflect.<br> I called back this morning and was told different stories of why they cannot reverse the transaction. I made contact with the merchant who informed me I will have to contact my local bank to cancel the transaction. I went into the Mutual Park branch and connected with the Authorisations call centre. Innocent (think that's his name) first needed to enquire with his team leader on whether he can reverse the transaction? Since when must an instruction from a client be approved by a team leader? <br> When they reversed the funds I was informed that should the merchant debit the account again, the funds will be made available. What am I missing here? Does the merchant have more authority over MY bank account? . IF I say cancel the transaction do not allow the debit does that not mean DO NOT RELEASE MY FUNDS?<br> HELP