There's some misconceptions at play here - you don't have a fixed term contract that will expire.
You have a rolling contract that is always subject to 30days notice, but has a minimum term - which is often confused with "contract end". All that happens when your "contract runs out" is that you're outside the minimum term and are able to upgrade, change to SIM-only or give cancellation notice if you want to.
If you don't want to, and are happy as you are - do nothing and nothing will change save for a 10% discount after 3months. The only reason you will re-enter a new 24month minimum term is by virtue of upgrading your phone, or changing to a 2year SIM-only plan.
https://ee.co.uk/help/profile/leaving-ee/end-of-my-plan
