I had the steroid shots for the same reason, in the bottom 2 inches of my scar.
I tried all the creams and the silicone patch, etc.
The dermatologist first shot me up with some lidocaine (which itself burns) then shot up the cortisone. Lots of little injections up and down.
The itch stopped. However, I now have a depression in my incision area about half the width of my pinky in that area of my scar, where the tissue around the scar collapsed from the cortisone. It's a trade off, but I prefer it to trying to surreptitiously rub at my itchy scar, under my bra, all day long for ever and ever!
I don't know if it will ever fill in, but since a similar place in my ankle, where I once got horse kicked, has filled in over the last 20 years, I expect it will, eventually.