No need to change your number
Changing your phone number when you are getting anonymous calls on a regular basis is not a very good idea. Firstly this reflects that you are a big coward and in a way you are encouraging the bully. And what do you think, after changing your number, you will be at ease. NO! Not at all, he will again get hold of your new number. Hence you should find out Whose cell phone number is this? This is how you should tackle the problem. Trace down the number, get complete information of the caller and give him a dose of his own medicine.