Planetfitness..quick to sign you up, but will take you through hell to cancel your membership

I have been trying to cancel my wife's membership since 3 April and after a few email exchanges and phone calls, I received an email on 8 April. This mail from Planetfitness Customer Services dated 8 April confirmed that her membership was due to be cancelled on 30 April and that the last payment will be required on 1 April for her monthly membership fee, on condition that she calls their Customer Service. My wife apparently missed some of their phone calls, but she sent an email on 16 April to confirm the cancellation.

To my surprise, they also deducted the full membership fee for the month of May. According to the Manager at their Queenswood Branch, I am supposed to pay for the month of May as well as we are on a month-to-month contract. Someone at Planetfitness must please explain to me the purpose of their 8 April email and why I had to be billed for May as well