I collected all stamps around 21/9 (14:00 GMT)
However I haven't got the witcher 2 email key

I believe there have passed many hours for the email to arrive.

I am starting to get hopeless because the promo ends at 25 November exactly

( I checked spam/bin folder , Haven't changed email related to this gog account since the creation of account)

And I don't think my email provider is playing tricks on me (never did the last 5 years)

Is anything else I can do rather than waiting?

Can the key be sent manually by GoG.Com Support Staff?

Thanks for reading this

Contact support - http://www.gog.com/support/contact

As long as the stamp collecting graphic shows "ALL STAMPS COLLECTED We'll email you the gift soon" you're fine and the system scheduled you for a code for Witcher 2. The mails are automatically sent and you're not the only one waiting for several days. I waited 2 days myself and others even more. As you already contacted support, you've done everything you can for now. Don't expect them to answer immediately, because there are tons of support request due to the sale right now. If there really went something wrong with sending the key automatically, GOG support will for sure solve the issue as soon as they can, don't worry, just be patient.
If you receive the usual GOG promo mails, you don't have to worry abut spam filtering either, but if you never receive any mails from GOG, check your email provider's spam filter and add any mails from *@gog.com to your whitelist.