Upgrade erroneously done

MTN's contacted me to do an upgrade. I told them that if they are an outsource company I do not want to talk to them further. This person promised me that he was phoning directly from MTN. Needless to say the upgrade is a complete disaster. Nothing is working the way it should be and when I contacted MTN they keep telling me the outsourced company must handle the complaint and resolve the issue. I need this matter resolved asap