They may send you a letter saying if they didn't receive your response in written, then the plan is valid. I am a victim of Just Engery. They said they were from Hydro one and looked at my bill (that happened years ago). They gave me a impression that Hydro one also had some energy plan.
Unfortunately, that was a scam. I found "Just Engery" on my bill. I called in and was told it was a five year plan. Next year is the fifth year. I'll make sure it is canceled.
Just to share this with new house owners.