After reading through this thread I think its safe to say you need to sort this service out.
Nowhere on your donation page does it mention that activation isn't instant.
Please take this as advice. By Paypals terms what you're selling is considered "not as described" and if enough backlash is drummed up it could lead to account suspension or worse.
Either make it extremely clear at the point of payment (not in a forum post) that it's not instant or actually make it instant.
I'm happy waiting a day or two for activation but people should not be waiting 3+ days for a digital product that they legally own.