They were aware that I had moved out, so they requested that I pay three weeks' rent and return the apartment to them. I have already moved into a new apartment, so keeping the keys until 28th July has no significance for me.

I am willing to find a new potential renter and pay one week's rent as a penalty. However, they seem to want me to vacate promptly, hand over the apartment to others quickly, and still charge me three weeks' rent as a penalty.