Mobile pass or not? I guess so.
The pass is activated when you use / fill out first trip (afa i understand, have never used these). But you have 1 full month=till 18th march if you did have 19/2 as first day.
Otherwise you have to contact help centre for a reset-this can only be done mo-fr office hours
You have to contact the Customer support by this form https://eurail.zendesk.com/hc/en-001/requests/new Facebook or Twitter The Customer service works every day :)
Thanks for your responses!
For all whi might have the same problem: I did contact the customer service and they responded me (on a sunday) within some hours. I send them a Screenshot with prove that I didn't book a train for that day and they added an extra day on my interrail ticket. So, luckily it all worked out for me :)
For any next journeys: do not activate a travel day unless you sure you’re going to use it. There’s no need to do it in advance.