As several others before, there seems to be no way for me to enter my 2 redemption codes on the website :( How could this be solved?

When I follow the instructions, I get taken to a checkout page with a pre-entered code from their current sale with no way of entering anything else.

Pretty frustrating... and since there have been others with the same question in the last days I don't really get, why you don't post a solution to this, instead "pls write an e-mail"... which I did, no answer yet.