Charging from bank account despite contract being formally terminated

My contract was formally terminated in Dec 2020 as I left Germany for good. Indeed, it says so on my Online O2 account that it was terminated. However, O2 has been charging from my German bank account. Next bill due to April. Likely they will keep charging. As I live now in Switzerland, I don’t check that bank account so often and therefore only realised now. Tried to contact O2 multiple times but it’s always busy. I’d like to sort this problem ASAP. Please get in contact if you please Thanks

Edit by o2_Katja: Verschoben in unseren Englischbereich