Your in-room fridges have, let's face it, a pretty small freezer compartment. If you want more, you could ask for a freezer space. Freezer spaces cost a few Euros, not much, and you'll have your own in the basement. You might want to put a lock on it, if you're concerned about people stealing your food, but the area is camera surveilled and u.city residents are nice people.
Open a ticket, if you're ready to have this done. You'd buy the freezer (a good sized one costs about €250), u.city installs it, and then it's all yours.