Tenants requesting new furniture after moving in for a few months

[Suduk N.]

A tenant who has moved in for a few months to my fully furnished apartment in Chicago and had quite a lot of requests and complaints recently made a request to change the mattress after sleeping on it for months and claim it's old and needs to be replaced.

I kindly replied to say they could get their own mattress. They said they want to reduce the rent if they need to buya mattress themselves. It really pissed me off with the ridiculous demand after moving in for months and also the rent is low and they are expecting high end rental. 

If they deduct the mattress cost out of the rent this month, what's my option? Also i want to terminate the lease early with them to save me headaches with requests every other week. There is no clause in the lease for me to end early. What could I do? Thanks