Activation ID?

[MetalPhoenyx]

Greetings everybody!

First of all, I do apologise if this is not the right place to ask this, I'll perfectly understand if the moderators decide to delete this topic. The truth is, I don't know whom to turn to, therefore I'm taking the risk.

Basically, I subscribed to Sibelius Ultimate a few days ago, and have been trying to join the official forum, with zero success. Here's what the "join" page says:
Please enter either the serial number or activation ID for your copy of Sibelius.
I've typed, retyped, copied that code hundreds of times already, did it with or without hyphens uppercase/lowercase letters and pressed "Next". Always the same result:
The following errors occured
• Activation ID not valid

I swear I'm not illiterate, there's no mistake in the code. It starts with "SB" and it's a series of 4 times 4 characters. Unfortunately there is no contact email on that page, they really offer no alternatives.

I'd be extremely grateful if someone could give me the smallest hint, what on earth am I doing wrong?

Many thanks in advance, wishing everyone a nice weekend ahead.