We have got 21 license from last year and now we are added more workstation and will buy 15 more license.
is it possible to combine old license and new license?
i need it to be combine because we are using avast SOA.
Contact business support.
https://support.business.avast.com/hc/en-us
i already contact business support since june 15 but only bot and no actual support respond to me.
Have patience.
re emailed no response 
As I said have patience and do not create new tickets as that will put you back to the bottom of the stack making you to have to wait longer. (FiFo system)
This is something for avast to look at as only they can see the licenses (and other details).