Double debit

Hi,I have agreed with MFC to debit their money on the 15th of every month now last month on the 15th of may 2019 they didn't deduct as we were making arrangements for the balloon payment .we then agreed that they would start debiting from the 15th of June for the months that I have requested .then on the 30th they debited money without my consent unfortunately there was nothing on my account I sent an email to rectify that .they rep**** and made amends after two days I received a call from a rude consultant claiming that I'm in arrears. I tried to explain she wouldn't listen this month they debited twice I would like to understand why.Thanks