Child Registration

I've been trying to register my child's microsoft account for 3 days. Every time it asks for me to sign in and verify my age, and I enter my credit card info and click ok. Then, this error pops up: "There's a temporary problem with the service. Please try again. If you continue to get this message, try again later." I've tried again later countless times and talked to 4 microsoft support agents but none have helped. I tried changing web browsers, changing my account security, and entering different credit cards to no success. How do I get past this issue?