Former tenant is mad I cashed their rent checks?

I was renting my house to a family. They moved out the first week of August. They had financial problems and had only been paid up through June. They wrote me checks in early July to cover the remainder of the lease (2 months rent) but told me to wait until July 31 to cash the checks. They then told me to wait again until Sept. 15 to cash the checks. I nearly missed paying my mortgage on that house so I decided I needed my money and cashed the checks early. Now the're in a fit because they said I wiped out their bank account. Was it wrong to cash checks paid to cover rent after they've already moved out?

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