Hi Goncalo - it looks like you unlocked your Strava bonus on Nov 22nd, 2015 which is why it just expired. Per the message, Strava Premium entitles you to 2 consecutive free months of Zwift once every 12 months.
Don’t worry, you’ll get your next 2 Free month bonus on Nov 21st this year.
If you experience any further issues, please submit a support request and we’ll be glad to sort you out. Ride On!