That is a great question. The federal Fair Debt Collection Practices Act does not specify how many calls collectors may make in a day or in a specific period of time. It has been left up to the courts to decide whether repeated collection calls can be considered harassment.
We would recommend you use our Free Debt Collection Worksheet to keep track of collection calls. If you suspect the debt collector is calling repeatedly to harass you,it doesn't hurt to talk with a consumer law attorney. If you have been keeping track of these calls, it will make it that much easier for the attorney to help you.
Since you live in California, you could certainly contact the co-author of the California edition of our book, Robert Brennan, at BrennanLaw.com.