Tried this as well but get the same result, account number not recognised. This info section below that tells you where to find your account number also states it's 9 digits which means it shouldn't need the prefix (at least not for my account number).
Glad it's working for you though, lets hope the email support address gets fixed/enable soon for the rest of us.
I did the thing where you put the area code before the account number and now I get the error - It looks like you’ve already received your exclusive Destiny 2 Sparrow code. Hope I haven't messed things up for myself and I still can get a code..
Once they sort out the issues with the page and contact email address you can ask them to deal with that problem
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I tried this, and now I get this message ' t looks like you’ve already received your exclusive Destiny 2 Sparrow code '. I know no one else in my household have redeemed the code, as no one else plays Destiny, so I have no idea what's going on there.