Email contact

Hello,

I need an email or any digital medium to contact the customer support area. I had an O2 contract which I cancelled before I left Germany in December last year. I'm still getting invoices of outstanding payment, but before I left I went to an O2 shop to cancel my contract with my deregistration from Berlin since I was leaving EU. I can't send post nor make a call to Germany, which digital medium can I use to solve this issue.

Best,

Juan Roca