Took off double the amount then what was agreed

After having spent an hour on the phone with Nedbank last month & having had or presumed good services & hopeful that now after all the fuss things will go right & the problem solved. Wishful thinking. Spending time with customer services last month we agreed on a set figure to be taken off for 2 months due to their error. Only now they took off double the premium. 1 payment went off on the last day of the month as agreed, now it's paid, but to my surprise this morning I see another sms that Nedbank took off another premium (guess when) on the 1st of the month at 01:30am. Excuse me. Nedbank completely disregarded the arrangement & agreement & as far as I am concerned breach of contract now too. I am done dealing with your customer services because they cannot do what is asked & nicely at that too. I am going to my bank & reverse the extra monies you took off my account, I am writing Nedbank a letter to cancel your debit order as you no longer have my permission to take money off my account & I am taking that letter to my bank & I will put a stop order on your debit order. I prefer to pay Nedbank myself, then I know it is paid on time every time. This is not Mrs Pillay's fault...