Unless you agreed to this arrangement in your lease it is not legal. You can sue to recover the amounts you have paid that you can attribute to common-area usage. If this is a 7-unit building in Chicago, you may have other rights against the landlord under the local Ordinance. An attorney in this area can help you determine if those kinds of rights apply.
This information is general and does not constitute legal advice, or create an attorney client relationship.
Withholding from your rent could cause you to be evicted. I would call the electric company to get their portion rewired to their own meter. You could sue for reimbursement in your small claims court.
I agree with the above answers, and would add that this unit would likely not be covered under the CRLTO because it is an owner occupied building with 6 or fewer units.
This answer is intended as informational only, and does not constitute legal advice or form an attorney-client relationship between us.