In order for a collection agency to collect from you, you have to admit to the debt over phone or by letter.
Legally you did not sign a contract with the collection agency, their job is to use whatever measure to get paid by the debt they purchased from a company, debt you owe or used to owe that company.
Paying a collection agency does not clean up your credit report. How you decide how to pay off will affect how long it remains on your credit report.
By not paying the collection agency, they will continue to phone you and they might even take you to court, if they don’t take you to court the debt is purged from your credit report six years from the last activity. By not paying the debt is removed one year earlier than if you paid the collection agency. (this method is not recommended).
Through a not for profit credit counselor you pay full and the debt will be removed in three years and last, if you file a consumer proposal, if qualified, you pay less and can be clear of debt in three years after the final payment.