Mtn and *****

Mtn are allowing ********** access to their systems, I received a call from a so called Mtn consultant , he had all my Mtn account details, cell no , info about a sim i have for data etc, they were able to generate a OTP on the MTN platform to trigger a required response from me the end user. How can this be described as secure, if one response to the consultant(you shouldn't) you become a victim of *****, why do these have access to the Mtn systems to initiate the process in the first place?