The upgrades work by giving you the new access level from the date of the first purchase.
e.g. you buy Silver on 1 Jan and then on 1 March you buy the silver-gold upgrade then you are entitled to Gold until 31 December (i.e. 12 months from the original purchase). The reason for this is that otherwise people could buy the silver-gold upgrade on the day before the silver expires and basically get a year of gold for the price of the upgrade.
In your case if you'd upgraded from silver to gold before 13 Feb you would have had gold access through to 13 August.
If you want continued access to the support forums and club downloads then you should now purchase either a new silver or gold membership.
Hope that makes sense.
Geraint
p.s. You can of course continue to use the addons you have downloaded so far with no restrictions and buy a new membership at a later date when you want to upgrade or need to ask a support question.