Tenant paid previous property manager

[Keaton M.]

I just bought a fourplex and we closed around the 20th of last month. I sent an introduction email and notice that online payments are changing. Now rents are due and the tenant said they paid the previous property manager before seeing my message and their payments were set up on automatic bill pay. 

My question is how do I recover the money from the other manager and what can I do to get them to hustle. I've already called and emailed, but havent gotten a response. It's also July 3rd so they'll probably drag their feet for the holiday weekend. I've also instructed the tenants to contact the manager as well. 

Thanks for any input.