Unable to un-invite Guild member

I accidentally sent a guild invite to the wrong person (to someone I don't know) and I see no option to cancel the invite.

This is a problem because I just spent $5 on points and got a Premium Guild Stash Tab. I'm concerned that the person may accept the invitation and take items from the stash.

Leaving the guild and creating a new one is not really a viable option because I have already invested real money in the guild.

Can anyone help with a solution?