You are right , the 500 mins plan was replaced with 700 mins , and that 700 mins plan on the main site no longer appears available to order ,( it’s PAYG or Unlimited ) in my opinion the BT website is pretty poor with pages that contradict each other , show old or no longer available options etc ( it must be a mammoth task to keep each entry current ) , £18 is the list price for Unlimited calls , there was a recent post where someone negotiated that call plan for £12 , but as far as the page you have posted , I suspect it’s simply a page that shouldn’t exist or be accessible
