Banking details changed with no consent!!!

This is a very deep concern for me to know that without consent or verification my debit order banking details can just be changed without verification or confirmation. I have had a Teljoy account for the past 2.5 years now and not once have i had issue with my debit order going off. This month when my debit order was supposed to go off it didnt, when i checked my Teljoy profile the banking details have been changed. So my question is who gave consent, and how did they get the banking details from in order to change it on my side. My account number has not changed or i have not given directive to change any banking details. This is very worrisome and concerning, and Tejoy can not provide me with a concrete answer.