How do I know if my contract is canceled?

I left Germany for good over a month ago. Before I left, I canceled my o2 contract with 3 months advance notice, effective 30.04.2016. I have the confirmation in writing (although I can't find it right now since things are a mess after my move).

I've just received my final bill for the period 25.04 - 25.05.2016. Alright, let's hope that's the last one. But how can I tell whether my contract is actually canceled? When I look at my "Tarifdetails" under "Mein O2", it shows a contract with Vertragsbeginn: 01.06.2016 and an empty Vertragsende. What?? Do I somehow have a new contract open??

I'm not sure why you force me to ask my question to the community instead of to o2 customer service. I'd only like to hear from o2. Thanks.