Oneplan Health Insurance
Policy cancelled - money still taken from account

I cancelled my policy with ONEPLAN giving more than a months notice.
After numerous calls and emails about my cancellation with ONEPLAN, they continue to deduct money from my bank account, last month and this month.
Now they have debited double the amount from my account and it is a struggle to get this back. Leaving me short for my other debit orders.
It costs me money to put a stop on this debit order and banks charge for reversal.
I received phone calls from them asking me why I cancelled. So, somewhere one department is not communicating with the other department.