How do u trace number when its been blocked?

Contact your provider and report the calls to their security group.

Your provider will be tracking calls on their network for billing and airtime purposes. They should be able to trace the originating number if you can tell them the date and times of the calls to your cell. They can then block that number for you.

Yes, you can not personally tract it, if it is harassment, you notify the police and the service provider.