I already tried this. And it doesn't work, which is why I am very frustrated.
I tried calling online customer service, which made me wait more than an hour. I was then transferred to sales but in the process, there was a mistake and I was back to where I started and asked to wait for more than an hour to reach the online customer service again.
This is not acceptable, and should be fixed so that people can purchase credits on the menu as you have pointed out.