Hi Pradhan,
I would suggest you try disabling the firewall policy on the SEPM and then activate NTP on the client that is having the problem.
If you still can not access the website then the problem might be with IPS.
If you can access it, then it's definitely one of your firewall rules that blocks it.
Make sure all rules are set to log matches to the traffic log.
Then enable the Firewall policy again. Try going to the website and then check traffic log.
If the firewall blocked some packets because they matched a rule, you will have an entry in the client's traffic log, the last column will contain the "guilty" rule (which you can then rethink)