Hi,
I am guessing that the payment gateway integrated is one of webpay or payu (Just a guess. Could be any ass there are many naira based payment gateway).
As a Nigerian software engineer and web developer who has faced this sort of issue many times I have over 12 years of experience in software engineering and over 8 years of experience integrating payment gateways into Nigerian websites.
Let me help you solve your problem. Chat me up and let's start working ASAP.