Most, if not all collection agency efforts are governed by the Fair Debt Collection Practices Act. In this act:
1. A collection agency may not contact you at work. the actuall wording on the FTC website is ” A debt collector also may not contact you at work if the collector knows that your employer disapproves of such contacts”
2. A collection agency must stop contacting you if you send this request in writing. “You can stop a debt collector from contacting you by writing a letter to the collector telling them to stop. Once the collector receives your letter, they may not contact you again except to say there will be no further contact or to notify you that the debt collector or the creditor intends to take some specific action. Please note, however, that sending such a letter to a collector does not make the debt go away if you actually owe it. You could still be sued by the debt collector or your original creditor”

So you should definitely write a letter to the collection agency requesting that they stop contacting you. You still will have to fight the debt, that doesn’t go away.

Yes the Fair Debt Collection Practices Act also covers the term harrassment. Here is more from the website:

What types of debt collection practices are prohibited?
Harassment. Debt collectors may not harass, oppress, or abuse you or any third parties they contact. For example, debt collectors may not:

use threats of violence or harm;
publish a list of consumers who refuse to pay their debts (except to a credit bureau);
use obscene or profane language; or repeatedly use the telephone to annoy someone.
False statements. Debt collectors may not use any false or misleading statements when collecting a debt. For example, debt collectors may not:

falsely imply that they are attorneys or government representatives;
falsely imply that you have committed a crime;
falsely represent that they operate or work for a credit bureau;
misrepresent the amount of your debt;
indicate that papers being sent to you are legal forms when they are not; or
indicate that papers being sent to you are not legal forms when they are.
Debt collectors also may not state that:
you will be arrested if you do not pay your debt;
they will seize, garnish, attach, or sell your property or wages, unless the collection agency or creditor intends to do so, and it is legal to do so; or
actions, such as a lawsuit, will be taken against you, when such action legally may not be taken, or when they do not intend to take such action.
Debt collectors may not:
give false credit information about you to anyone, including a credit bureau;
send you anything that looks like an official document from a court or government agency when it is not; or
use a false name.
Unfair practices. Debt collectors may not engage in unfair practices when they try to collect a debt. For example, collectors may not:

collect any amount greater than your debt, unless your state law permits such a charge;
deposit a post-dated check prematurely;
use deception to make you accept collect calls or pay for telegrams;
take or threaten to take your property unless this can be done legally; or
contact you by postcard.