Planet and Debt collection

Hi All, So I Canceled my membership with this Gym 3 years ago and today "14-12-202" I get an sms from Saya debt collectors on the behalf of Planet saying i owe them R1277.76 so I called Planet and they telling me is the unpaid membership of 2017 around June with interest i assume, and they cant explain to me what took them so long to get in touch of me ever since I left them 3years ago, no answer was given but I suspect that they wanted the so called debts to escalate so they can cash in on the interest. i think this Gym is just trying to take advantage of people...