DSL Contract Extended after cancellation

Hi

I posted this in the German discussion forums (in Deutsch) but never got a reply, apart from a helpful citizen, so I’m trying here in the English forums

I cancelled my DSL contract online in late September, and followed up with a phone call to confirm a week later, in time to meet the deadline for the end date in January. 

At the time of requesting the cancelling on-line I didn’t receive an email from o2, just the message in the myo2 portal that i must phone to confirm. 

Now, a month after cancelling, I see that I am still being charged for DSL, and furthermore, my bill says that my contract runs until 04.01.2022 - and re-checking the email I received after cancelling on the phone I can see that indeed the cacenllation was processed for 2022. 

I still have my mobile with o2, have actually just extened my contract, but am really very surprised that this DSL contract has been renewed, even though I have done everything I can to cancel it with the time limitiations.

How can I have this DSL contract termitated for the date i requested, January 2021, and be refunded for the two months I have now been charged for it? 

Please can someone help?