Harrassment, bullying tactics! Horror service

I signed up for a three year contract in August of 2016, which would have ended in August 2019. At no point did I extend that contract beyond it's maturity date.

Cartrack never contacted me to negotiate an extension, nor to discuss any issues regarding the contract. I have stopped making payments.

Subsequently I was contacted, where upon I indicated I do not wish to continue with their services. Their consultant called to arrange collection of cancellation fees because I supposedly cancel the contract before it ended. He promised to investigate the matter and provide me with feedback. Instead I've been bombarded with sms's demanding payment of the cancellation fees. Today, I'm threatened with legal summons at my work. Is this even legal? If anyone knows where I can report this please help.