If you've tried cleaning mould from silicon previously, the mould has likely stained it. If this is the case, no amount of scrubbing or applying cleaning products will remove the stain from the surface.
Unfortunately, removing the silicone and replacing it with freshcaulkingwould be the best course of action.
If you are not keen on replacing the sealant, try 30 Seconds 1L Shower Cleaner.It might not remove the marks entirely, but it should make them less noticeable.
Before using the product, it is best to open any windows in the room and run the exhaust fan. Also remember your personal protective equipment including a face mask, gloves and safety glasses. - MitchellMc
I have had success with using vinegar to kill and stop the growth of the mould and then using something like bleach to remove the staining in some cases.
The way I found to keep the liquid on the silicon is to using toilet paper or the like, spray it then push it up against the silicon to make it stay there and lesson it drying out so you can leave it there for a few hours. Never mix the two together though as it creates chlorine gas, wash well with water in between each chemical. - MrSober