Do you have the right number? I had a problem a while ago and I think it was due to having an old number to contact them on. Try 01724 747 670 (remember that the ticket office isn’t open for business until 10AM too).
You can also ping @SUFCTickets on Twitter. They respond pretty quick on there, at least they did for me when I wanted to sort out my daughters York City match ticket. And finally you can try the online ticket portal: https://www.sufctickets.com/scunthorpeUnited/ASP/bookTickets.asp?
and print off your ticket, save it to your phone, or show the email on your mobile when you get to the ground.