Back when my ex moved into my place, she verbally agreed to pay me $1000 per month in rent and would sporadically send me electronic transfers throughout our time living together. She moved out 2 years ago, we are no longer together, and do not speak to each other.

I recently went back through my records and found that over the 3 years that she lived here, she failed to pay approximately $12,000 in rent and I am interested in remedying this situation.

Unfortunately, I do not have any written documentation of our agreement (stupid, I know) and there is no email to text message exchange to validate this beyond our verbal agreement and the electronic records of her occasional payments. I know of a few people who could serve as witnesses, but that's all I currently have to work with.

I have emailed her about this issue and provided itemized information about the payments, but she has either blocked me or is deliberately ignoring these messages.

What are my options for recovering this money?

Edit: I live in Chicago, IL