To be fair- with his erratic behavior he may have not actually fired his agent (sending a nasty tweet doesn’t count)... and even if he did I believe there’s a brief window before you can hire another (cooling off period of sorts)
Firing the agent, allegedly saying he’d play at the right price and then saying the bills had til Sunday... leads me to believe he threatened and the bills said “sorry to hear that, let us know if your playing but it’ll be under the contract you just signed” and Ritchie then blew up his health problems.