Unfortunately, your plan is not feasible. For some time now, a tariff change to the Cable Max can only take place if the initial tariff costs a maximum of €39.99.
In addition, the Cable Max is a promotional tariff that is not offered continuously. None of us other customers can tell you whether it will still be offered in January 2023.
At most, you can submit a cancellation and, after receiving the confirmation of cancellation, call the customer recovery number contained therein (support only in German!). Under certain circumstances, they can offer the change, but there is definitely no other way.
