MTN Failure to assist with proof of purchase for upgrade

I upgraded my contract and when making calls on the new phone the connection is disrupted. I went into the store and they require a proof of purchase. Owing to the fact that the upgrade was done telephonic ally with an MTN agent named Johan, who won't take my calls or read my messages I am unable to obtain the proof of purchase. I have phoned the call center repeatedly, emailed MTN days ago and sent a msg on MyMtn and no response