A simple search of "refund" and confirmation in last Nov on main thread below shows there is a long standing issue of refund. The last update on this issue was about 5 months ago by a community manager.
People are either posting to the main thread or starting a new question about this. New questions get a reply with link to main thread.

1. Clicking Refund gives error and suggests you to contact Google Voice (this link bring you to this forum).
2. Clicking Contact brings you to this forum.
3. Contacting Google Voice via Google Wallet gets an automated reply linking to this forum.
4. Contacting Google Wallet support get a link to Google Voice support (see number 2) and you end up on this forum

This is going around in circles with no input from Google. Can we at least have a support address where refund requests could be sent which refund button is fixed?
People are losing trust in a paid Google Service here.

Main thread: https://groups.google.com/a/googleproductforums.com/forum/#!category-topic/voice/account-credit-security-and-privacy/O5U_TWt6VXE 

List of refund threads: https://groups.google.com/a/googleproductforums.com/forum/#!topicsearchin/voice/refund