For Québec resident
Here`s a few things to know and to write in a letter.
You can request that the agency onyl contacts you in writing (much less annoying than the phone), section 34 paragraphe 2.2 LRCC, valid for 90 days
They can`t contact you if they haven`t sent a "bill" sec 34 par. 1, or less than 5 days after sending one if you give them your current address (sec . 34 par .1.1)
They can`t tell you that they`ll sue you if you don`t pay (34 - 6)
They can`t charge interest or recovery charges (34 - 7)
Always cc to the Office de Protection du Consommateur and/or your local consumer association (btw these usually offer templates or even write it for you).