Some of the people on the NHS Overseas Services Helpline are helpful some are not. The information on the .gov.uk website says the following:
“How to use an S1 form in Austria
You must register your S1 form with the state health insurance fund (called ‘Österreichische Gesundheitskasse’ in German).
Once registered, you’ll be given a card called an ‘e-card’. This shows that you’re entitled to healthcare on the same basis as an Austrian citizen.”
As you are in Vienna I would call up the ÖGK in Wien and ask them what to do
Österreichische Gesundheitskasse Wien
Tel.: 05 0766-11
Fax: 05 0766-113003
The post from the UK takes around a week but we are getting close to Xmas. If you don’t receive your S1 by post then ask the NHS Overseas Services Helpline if they can send it to you via NHS secure email (egress).
Good luck and take care!