Hi,
From what I understand, this payment plugin was developed by the payment gateway themselves. So everything that is sent to pay2go is sent by that plugin which was developed by them. So unfortunately, I won't be able to help. I don't even have a copy of the code of that plugin, I never saw any integration documentation for that payment gateway and they didn't even tell you what was the exact problem...
I'm afraid you'll have to check again with their support for further help as I don't see what we can do to help you here.