Sorry you're running into issues getting your student entitlement.
You shouldn't need an email response from the store (though you should've gotten a receipt). If the payment was successful, the MAXON One entitlement should be in your MyMaxon account. You can check this by logging on at my.MAXON.net. The entitlement should be immediately available for use in Cinema 4D or Red Giant App.
If that's not the case, please send me a direct message with your MyMaxon email address and I'll track down the issue.
Cheers,
Rick