it's likely the employee who responded to your ticket/email does not know shit, I have never paid using paypal on Bitmain , they never asked me to, and I still got the credit after sending them an email.
It's at least two different Bitmain CSRs telling multiple people the same thing in regards to paying with PayPal and then requesting credit to be applied. Seems like that's their decided policy if your item hasn't shipped yet. I received the same exact e-mails you did. They said the credit was already on my account, but it showed nowhere on my account or after placing an order to apply it. When informing them this, they told me and others to pay with PayPal and then inform them of the order ID to have the credit applied, or you could wait until original order shipped and have them send refund in BTC.
Maybe they applied smaller credits to accounts directly or the only reason you received it was because your items already shipped? Coupons weren't supposed to be issued until after shipping. Majority of people asking haven't had their items ship yet and for those people they have been saying it's a hidden credit that you need to contact them to apply after paying with PayPal if you want to use it now.
I just checked my account, and there is still no credit showing and no coupons issued.