What did they say the issue was that they couldn't get him and forgot to call? Are you happy with the care and communication otherwise? All that would weigh heavily in how I felt. If your child had been left alone or unsupervised, I would be livid and say pull and report. But he was safe and supervised at school, just a little late for pick up
If it was a simple miscommunication and day care was apologetic and we made a plan for just in case, I would probably be satisfied.