Problem with activation of Adobe Elements upgrade 2020 to 2021

Hello

Today I bought an upgrade from Elements 2020 to 2021 on the official Adobe site. After the payment came a serial number as well.

The problem is, I cannot activate it. Every time I enter the serial number, the program tells me: connect to the internet and try again.

So, if I didn't have an internet connection, I wouldn't be able to write this either.

Customer service is not available from Fri 16:45.... Great.

Can anyone help?

Vlad