Unaccepted behavior

Nedbank debited my homeloan account 3 times and left my account on minus. I have payment arrangement that is in place they decided to ignore it. No one can assist me . Sipho Nkambule that is handling my account is not nswering my emails. I'm in desperate need my refund and no can assist. This is unaccepted behavior where the bank will debit my account as they wish.