@Retroprincess do you have a hot glue gun? If yes, I would try this - scoop out as much water as you can, then dry the sink thoroughly. Blob hot glue on the plug, but not going over the edges, and glue something like a spoon vertically on to it to create a handle. Let it cool thoroughly, then try pulling it up. If it doesn't work, the worst that'll happen is the glue just pops off