Upgrade letter connect to max package

Even though my exchange has been enabled for the Max service for 1 month I have been told by Sky Customer services I can't upgrade until I have recieved a letter asking me whether I want to upgrade. If I was a new customer I could automatically get it (after putting in my details on the sky web page), what worries me is new customers getting the max package and then being told there is no more capacity for any upgrades, as seen in previous posts. When I asked about an upgrade date I was told they didn't have any information on when it would happen.
Does this letter actually exist? and is this the only way to upgrade?

I would call again and req it again it depends on who you speak to it would apear with most issues