take a picture of it, document it, call the builder and document that, then be persistent.
In the mean time do not use the shower at all.
Now, this is not a big deal but IT should not have happened anyway and I know how I would feel also being a brand new home.
The foam, I could not guess. There should have been a hard gray cementious substance behind the tile. Do not know what you got into. I would save a sample of the "foam" and take it to a knowledgable person, not someone in a home center and find out what it is. Get his name, and company, and do it again somewhere else.
I presume that this is a ceramic tile shower enclosure. The hole has to be in the grout. I cannot imagine the hole in the tile. Get some premixed grout and with your finger force the new grout into the hole until it fills up. Smooth off the filler and let it sit for three days without any use. After apply the grout, wipe off the area with a damp cloth until all the haze is removed from the adjoining tile. Keep doing this until perfectly smooth. Use your finger to smooth out the patch and make it look like the others.
This should do it.
This remedy will take about three days in all with curing process, the litigation may take three months. Your call.