PLANET FITNESS THREATENS PEOPLE

I cancelled my membership about 6 years ago and all of a sudden I am getting collection agents after me as someone seemingly, in the Planet Fitness accounts department, forgot to stop invoicing me per month for 6 years. Over R17 000 they are trying to ****** me for. I am being threatened and bul**** by them to pay money that is not due. Why after all these years, threaten me without cause. Are they gangsters looking to make money off the innocent?