I had the same problem a week or so back. The phoning thingy is flaky (faulty) and you need ebay's help.

I was in a chat session and they got it working with my mobile, using the format (04) 12345678 (2 digits then 8 in the next box) rather than (0412) 345678

If you can't make it work, just click on Customer Service at the top right of this page, then choose Contact Us tab, select Account, then Registering and then click on either Chat with Us (online) or Call Us (by phone). DO NOT use email, it;s a waste of time.