If pre paid cards don't work (not 100% sure if they do or dont) you can always connect the pre paid card to a paypal account and buy it through that.
No it’s instant. Not sure if @Opalium or @Highwon handles all that shit now but they can help you out more than I can.
It may be an issue more with you trying to buy it as a recurring payment, im guessing most prepaids since they are not actually linked to an account probably wont allow a payment to be automatically accepted, are you selecting one time payment or recurring?
I know from past experiences that there should be a website on the card, you probably have to visit it and enter a postal code for online purchases @Beta_Ray_Billl