Hello, I have purchased two Interplay games, during the time of the promo but did not get my bonus code for either one. I tried sending emails but for the last several days have got no response. Thanks

you must remember the rules.
1. You need to have signed up for the Early Access Beta between July 10 and September 7.
2. You have to register an account at GOG.com with the same email address as the one you've signed up with.
3. You must place your first order during the Early Access Beta, between September 8 and September 21 at 11:59pm (EDT).
4. You have to love classic PC games!
my guess, you didn't follow number 4.

Yeah I met all those requirements. I only get the order invoice(s) in my email, not the bonus code.

It's also been rumored that you have to have only 1 game in your cart for your initial purchase.

Indeed, I purchased Descent and Shogo on two seperate orders

That's not true, it's just your first purchase. It can be every game in GOG's current library/

emboldened for truthiness.