Here's my simple (possibly painfully complicated :)) process:
(pardon the hastily drawn up blog post with terrible screenshots and indentations)
- Go to your Microsoft account page
- Select Service & Subscriptions
and select show more
- Get more Gold
- (as an aside, I currently have 30.5GB free space on OneDrive but MS is reducing that to 5GB ... good luck to all the businesses running Office 365... MS isn't showing much favorable behaviour at the moment. They've even acquired Sunrise calendar and now they're discontinuing it :( ).
Choose your subscription, then follow the confirmation prompts, and voila! You'll get no confirmation of the purchase and will be dumped at an Xbox settings home page, none the wiser ...
To verify your subscription status, go back to the Services & Subscriptions page and confirm the new expiry and renewal dates. The best thing about doing the R50 monthly thing is you won't be screwed royally if you accidentally forget to cancel the auto-renew. You'll get enough warning to cancel it yourself before you are hit with a massive 12-month subscription price increase... you'll suffer one month of losses but that's better than the equivalent 12-month subscription auto-renewal coming off your account.