Licence revoked - help

Dear Adobe Pros,
I need you help please. I used to have a CS6 licence, I've bought it 2018. For almost two years I used another licence on my computer from home office when I was employed by a company. I resigned a few weeks before and I want to use my own licence from now on. But I can not, I got an error message stating "the serial number you entered has been revoked".

What can I do now? I still have the purchase receipt of my licence.
Thanks you for your help in advance,
Best regards,

Zsuzsa