Pending transaction REVERSAL!!

I need a reserved payment to be released back into my account because the merchant has already received their payment via debit order. Why does this cost me money to do when the mistake was with the merchant??? And why does it take so long?? I have my birthday in The next few days and FNB doesn't want to assist me in speedily releasing funds that is rightfully mine??? The merchant has wiped their hands off of the situation and the payment sitting in my reserve / pending transactions. They said they will not be banking the amount because they already received a payment from me SO WHY DOES IT NEED TO BE DISPUTED WHEN THE FUNDS ARE STILL PENDING AND NOT PROCESSED YET. I need assistance because im tired of the back and forth. I need my funds in order for me to go forward with my birthday celebrations.

One payment was debited and the other was a online payment made using my card details. I received no proof of payment, no decline receipt or any other information besides my sms notification stating payment was reserved. I cannot attach a proof of payment to the dispute form because none was received. I can't figure out why it's such a impossible mission to get my funds back that has not even been PROCESSED YET