Unfair blacklisting

Hi,<br> <br> I took a contract with Nashua Mobile, I was due for an upgrade and someone *******ly upgraded my account, went in to a Nashua Mobile store and collected the phone, the staff at Nashua did not verify the person's identity<br> not keep a copy of their ID document. <br> I was informed that there was a ********** upgrade on my account and I was asked to send supporting documents, which I did. now MTN has blacklisted me because I refused to pay for the ********** upgrade that Nashua approved without validations. Are they allowed to blacklist a person because of their employees incompetence?<br> <br> Please assist.