Unable to make in-app purchases?

"Your purchase could not be completed. For assistance contact iTunes Support at www.apple.com/support/itunes/ww/."

I keep receiving this error message whenever I attempt to make an in-app purchase. I have tried signing out, and then signing back in with my Apple ID, I have deleted and then re-entered my payment information, I have even closed the app completely, restarted my phone, made sure that restrictions were disabled, performed another sign-out/sign-in and updated payment information but nothing seems to be working.

I only have 1 Apple ID. In the past I have contacted Apple and they were [somehow] able to allow me to resume making purchases, however, this time I have attempted to contact support on at least 3 occasions with no help. My payment information is valid and works everywhere else! I find this incredibly frustrating. Are there any helpful suggestions?