Wrongfully charged by MTN

On the 3rd of November I bought 7gigs ( 1gb per day for 7days) using my yellow bucks. A total of 6000 yello bucks were deducted from my account, but I only received 1GB on the 1st day. Next day I called MTN to inform them , the response I got is used it all up during the night, despite telling them that my data bundles were switched off during the night as I have a contact with MTN, so my night bundle were running during that time they insisted I used it all up between 12am & 6 am where I was asleep! Fine. Follow night I made I switch off my phone- in the morning I switched it on; boom no data again! I call again, different agent- now the story has changed. The new version is no you never made such a purchase! The lady insisted even though I know I did and clearly the records show that my yellow bucks were deducted. This is theft!