Contract declined and no reason given

So I app**** for a data contract yesterday and received a call today from the sales associate from the branch to say my application was declined. He had no idea why and could not give me advice on the next step. I had a contract with mtn not even two years ago that I cancelled after the two years were up and never once missed a payment. I have an above average credit score and am pretty disappointed that mtn is not approving a contract with me and is not telling me why.