Your comparison of debtor calls to the writers 'telemarketing' calls isn't valid. They are two entirely separate things. Yours (debtor calls) is regulated by the FDCPA, telemarketing calls aren't.
Federal regulations already give you the right to tell callers not to call you again, but enforcement has been light. Here is the link to the applicable FTC site on actions to take against telemarketers:
http://www.ftc.gov/bcp/menu-tmark.htm
And for New Jersey:
http://www.bpu.state.nj.us/
As for the original questions:
Q1) "Can I sue a company (AT&T) for harassment."
A1) Of course you can sue them... for almost anything. The real questions are: is it practical considering the cost and ordeal? No. And, would you prevail if you did sue? Probably not.
Q2) "What legal action can be taken against this type of harassment in the state of New Jersey."
A2) I have done a cursory review of the New Jersey Utility regulations and there appears to be little NJ specific processes available. This means that your actions would rely on federal law. And as noted above, that is very seldom enforced. The only real option you have is to file a complaint with the FTC (Federal Trade Commission) at:
http://www.ftc.gov/