Good day I have a problem with DMC collectors, they have debited in a wrong money in my account, when I try to reverse or refund the money

Good day I have a problem with DMC collectors, they have debited in a wrong money in my account, when I try to reverse or refund the money. It's hard for me to get a hold on them... I understand they are collecting but we as customers need to be attended everytime when we need assistance.. because if it's like this no one will take them serious am also not making sure to continue doing payments under them if I can be ignored for more than a week by their consultants. Hire people who will make us take DMC serious not make us feel like we are ****med now I need to return that money I don't know we're to start. ***