Refund for error top up of 1000

Mtn is sending me from pillar to post there is nothing I haven't done to prove that the purchase of 1000 was an error and that I need a refund urgently, my job is at stake because of them delaying, paying the refund, last communication they referred me to blue label who referred me back to them but are still not willing to help. Calling their support center is useless because those agents just dismiss my request from the onset.

Is this how you treat your customers mtn, I am not wealthy I need my refund desparately please assist.