Welcome to Justanswer.com, my name is ***** ***** I will do my best to assist you.
What are the specific games you are trying to purchase credits for?
My apologies for the delay in getting back to you.
Heres an easy way you can bypass whatever blocks not allowing you to make purchases on viva slots..
Get an itunes gift card, you can get them online or at a retail store.
Load the gift card balance onto your apple store account. Then, you need to change the default payment method on your itunes account to "none"
That way when you go to make the in app purchase, it will pull the fee from your itunes credit balance.. And not try to charge your actual payment method.
Other then calling apple and figuring out whats the reason your blocked.. This is an easy and effective method to ensure you can purchase game credit when you want.
Dustin S.Senior Technician and Network Switching Systems Operator / Maintainer.