It sounds like you have some solid evidence on your side. Anybody can sue anyone for anything, so gather your evidence, witnesses, if any, and present it in court. You might want to consider filing an answer as well if it is not too late. The judge just may side with you.
Actively practicing law in Texas. Inactive licenses in Arizona and Georgia. All answers are general in nature and no attorney/client relationship exists in this forum.
It appears that the offset for the electricity was provided for in the lease, so you have a strong case that this is not owed. Plus, they knew about and didn't complain about it for the past 2 years, so they have waived their right to this claim.
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You need to consult a local landlord-tenant lawyer immediately. At least here in Oregon, if a tenant has to pay for utilities that benefit others, there are substantial penalties to the landlord if the lease does not explicitly identify and alert the tenant to it. Absent legal requirements, however, I agree that you have a variety of arguments in your favor.
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