Company quits on sick leave and blocks business cell phones and access to company laptops what to do?

I was given three weeks' notice.
All access was blocked. This means that if I extend my sick leave there's no way to notify the company. What should I do?

You can call, send a letter, etc.

You then notify extension of the sick leave by phone and send the AU by post and an email to the general address. Just stop from your private account.

Don't you have your own phone to call work? As a rule, you have to send sick reports by post anyway.