Account Debited without My Permission

I Had a loand with Bridge loans in 2013, i had a standard bank account at the time i open an account with them, I since changed to Nedbank , I never gave them my Nedbank account, on June 2017 they went and debited my account with my permission, who gave them my new banking details, I would like them to tell me how did they get hold of my account after 5 years i had an account with them