Take photographs. Keep calling your Ex until he answers and gives you an explanation. Until that happens and you are satisfied with that explanation, your child is not to be in the GFs company. It's positive that your ex had s go at her. If it was 'just' rough play then she'll be more careful in future. But you deserve an explanation.
I put him to bath and saw two nasty looking bruises on his back (about an inch wide) each, one of a really angry purple color. Dc says that GF was lifting him to throw him on the sofa (as rough play) and that the marks are burns from their carpet. Apparently ex told gF off but still my child has bruises/burns on his back. what should I do? Ex doesn't answer his phone. I should add that I live in ex' homecountry and that DC will go to the swimming pool tomorrow and the bruises look bad.