1. Are you equipping correctly the wishbone? You have to click to equip it like gear and listen for beeps. Faster beeps means closer to the silver.
2. What is the seed you are using?
3. You say the world was spawned after the ice cave update so there should be plenty of silver. And plenty of ice caves but knowing the seeds, we can at least look it up on the seed generator to see if there are any discrepancies.
4. Alternatively, using an iron sledge hammer in places and getting a damage tick of 0 under the ground can be a good indication of silver there.

Silver tends to be in the elevations where you also find obsidian. Just have to keep an ear out for the proper beeps.