High bills, I have contracts that I don't know about

Hello everyone. I have this problem with O2. I only subscribe for 2 sim numbers and that was in Gifhorn in Niedersachsen. And now, I moved out from that city and found a job here in Neumünster. Last May 2024, I went to an O2 shop here in Neumünster to change for subscription in one of my sim cards and to cancel my subscription for the other sim card. The process went well. The worker had me sign a contract and wrote a note in the contract to come back next month for the cancellation of the other sim. So, come June, I went in the O2 shop again and surrendered the sim, but apparently, the worker then told me to throw the sim in the waste bin, but i asked him if that is okay and it gives no problem at all. He answered yes, no problem. I left the shop thinking that my subscription had already ended and it won’t appear in the next billing. Apparently, that did not happen. The other sim card is still open and active. I went there again and complained that my subscription is still active, and why it did not end.  They said, that I need to send a letter to Customer service and write there to cancel the contract of this and that. I did not do that, hence, i made a cancellation via online. it went well through the process, but the problem is i did not receive any email from O2 if it was cancelled already or not yet.

My second problem with O2, in my monthly billing it shows additional 2 mobile numbers that i am not familiar with and i don’t have it physically. No physical contract was signed at all, but was included in my billing. That’s why my monthly bill is high. I complained about these two unknown numbers to customer service via chat online. The CS told me that I concluded the other number by telephone and the other was concluded in the O2 shop. I don’t remember calling any O2 shop concluding such and going to a shop concluding it without any contract at all.

I already sent a mail via Post as what the CS advised me to do and waited 7-10 days. It’s been over 10 days and i still did not receive any mail via post. I need help with these problems. Can anyone advise me on what to do next?

Edit o2_Kathi 03.01.25 Separated from another post and created own post