Thank you everybody so much for your input. We tried the Hydrogen Peroxide (we use that to treat our well water so was at hand), unfortunately to no avail.
Winemaker2 Don = THANK YOU
We used the sandpaper and OMG, it was like night and day and shocked us how we were able to remove the deep purple stain, and now there's just a faint yellow outline type stain similar to others where ornaments sat that we were able to remove somewhat to make hardly noticeable. We will be doing that with baking soda and vinegar again later on today.
For now though, it is so so good not to see such a glaring plum colour on our white window sill staring at us any more. Feels a little rough where we removed it with the sand paper but will try fine something to buff it back up if we can.
So THANK YOU everyone for you efforts. For us the Sandpaper did the trick for the most part Don