I jumped ship to Astraweb to save $£ a while back, but from memory it's secure.news.giganews.com or, if you're in the UK (which I assume you are), secure.news-europe.giganews.com
Try those, on either port 563 or 443 (both will work), and remembering to set SSL to enabled in your client. Failing that you can download and use the Giganews Accelerator from their website, and that will handle SSL for you. You'd need to change your news client's server to localhost:119 though if you did that.