I was the agent of a large collection agency - one of my many past lives.
If you owe money , they do not require authorization from you to
collect - no one would ever give such authorization.
Provinces limit when calls can be met but haraasment would have to be proved to be beyond a reasonable course of action.
GENERAL RULES
To avoid most action beyond the first nasty letter or call:
1) meet with the agency
2) offer some payment over time
3) it is easier to do that by mailing in a ( POLITE) letter stating your circumstances only permit $... per month and enclosed are twelve post dated cheques.
4) The agency I worked for always tried to get it all in one payment - but after a lot of bluster ALWAYS accepted a reasonable offer .
The collection agency gets paid for money received , so a reasonable offer allows them to set your file aside and concentrate on people who refuse to answer /pay .

