When did you purchase your license ?
You could also try sales @ avast.com without the spaces.

If you purchased avast Pro on-line you will have had your license and payment dealt with by share*it they should have sent you an email with your registration key.

Is this where you purchased your Professional license http://www.avast.com/eng/how-to-buy-avast-professional-edition.html ?
If so then this link from the above page might help http://shareit1.element5.com/ccc/index.html?publisherid=26451

Or did you buy it from a reseller & Distributor (http://www.avast.com/eng/distributors-and-resellers.html you would need to contact them) or directly from ALWIL Software (exceptional circumstances).