Are you sure that you haven't bought anything from the loyalty shop or solomon's general store? because Jagex won't deliver you any of these things for free
Just go check the loyalty shop, see if you have any items. Then check solomon's general store
It's usually the general store that pops up asking for space
If that's still not working, then you have to send Jagex a message telling them about this problem, they'll see what they can do.