It depends on when he made the contract is all. Pretty sure, though, it happened after they switched souls and after Charlotte was already in love with him so Mephisto has no reason to make a contract with him if that was what Vestia was trying to achieve. So in other words no I don't think the contract was fulfilled.
Ohh, I see, I see. I thought it was before the switch, and Mephisto is the one responsible for making the original Charlotte fall in love with the duke. However, Mephisto wasn't able to fulfill the second condition, which was related to the sword, since original Charlotte died so he made a contract with her to turn back time or something. I wonder why the conditions for the contract changed though. Or why a contract was made if there was none before.
She's not really the real Charlotte and the real one is already in the Princess' body... Sooo is it still applicable to her? Also, the duke's contract with Mephisto (the one about making Charlotte fall in love) is technically fulfilled too, right? Or is that a new one?