pending comment

Hi,
I have a comment pending and I cannot remove it. Everytime I click on ‘spam’ it just disappears for a second and reappears again. It does not go to the spam folder, it just stays there.
I have spent hours looking for a plugin to remove pending comments, but the only one which seems to have worked in the past is no long being maintained and is not compatible.
Any help would be much appreciated, thanks ??