FNB and your partner DMC attorneys are pathetic

I took out a personal loan with FNB (which is my bank) and gave them a debit date of the 20th of every month. They kept on deducting correctly until 3 months ago. They started trying to debit on odd dates and couldn't find any money. So granted they handed me over to DMC attorneys, I made an arrangement with them on the 19.12.2018. To my surprise I was debited twice by FNB on the 20.12.2018 and again today. I've been calling both DMC and FNB since yesterday with no help. The one company points to the other and I'm left with no money and no help. I'm the one making calls and still wondering if FNB and DMC will debit me concurrently. The requested arrangement letter that I received only today isn't acceptable by FNB. I vouched for this bank and now I'm in the ruts because of it. I'm a small fish with a voice though.