[Changed OS, do I need to buy new license?]

Hi, after latest windows 10 crash I switched to Ubuntu.
Can not register serial number, only for windows.
Do I need to buy a new license, or is there a way to change OS?
Thanks.

[[Solved] 3DCoat refuses to register successfully]

Yesterday I bought a copy of this application, installed without problems.
Put in the supplied serial number and clicked register, switched to a website informing me that the registration was successful.

But everytime I start the application it informs me that I have a unregistered copy and starts the countdown of the trial version.
Tried everything including re-installing, informed support with no reply to date.
 

Anybody here with similar problem and how to solve it?

Thanks in advance.