Removing a stain from grouting/silicon

Anyone got any ideas how to remove this stain from the grouting/silicon at the back of wash handbasin in bathroom - See attached pics

Have tried several things - Jif, Milton, Cilit Bang, Bleach. They've helped lessen the stain from a nasty black to a brownish colour but haven't got rid of it totally

Any suggestions?
Thanks

Pics are a little blurry, so it's hard to tell but it looks more like silicone. If so best cut it out and re-apply using a silicone with fungicide to resist future mould growth.