Termination of my contract due to moving abroad

Hello,

I lived in Germany for 9 months, but I didn't register myself at the city office, so I have no register confirmation. While living there, I got a 24 month contract with a new phone. There is still 6 months left on my contract till I can cancel it. But I moved out of Germany 11 months ago and I still pay for my contract, however I would like to cancel it. Is there a way how can I cancel my contract without having a proof of living in Germany? I live in Slovakia now and have a permanent residence here. Because of Covid, I lost my job and the contract is too expensive for me, but I don't mind paying off the rest of the contract if it's possible to cancel it.

Thank you.