License activation

I bought an new computer and installed Adobe Pro DC 2015 on it. On my old computer I signed out (i dont have a deactivate option). On the new computer I used my serial and my account to activate. But then there is a message telling me that the serial number is already in use on another computer. Support told me te reinstall Pro DC 2015 on my old computer and sign in- and out again, but after installing my old computer also states that the serial is already in use on another computer. I'm stuck now. What can I do to reactivate my license again?