How to keep O2 number from old contract when getting a new one?

contract has ended in October ....   renewed automatically.

sounds like a contradiction of itself. Ended or valid - thats a important question!

To move a phone number to another contract, order the "Rufnummernportierung" from your new account.

Did you terminate the contract you said ended in October? if not then it will have been extended automatically for 12 months. Contracts don't just end, so if you don't want it to be extended automatically in October this year you will need to send a letter to o2 terminating it at the end of the curent term. This letter needs to reach o2 at least 3 months before the end of the term.

Regarding the phone number, it is possible to transfer the number even before the current contract expires (cost: EUR 29,95). To do that you will need to ask for the number to be released. A moderator can do that here if you are patient. or you can call customer services. Note: The transferring of the number doesn't affect the duration of the old contract and you will be given a new number to use with the old contract.