No action on my cancellation request

I submitted a request to cancel my contract via their WhatsApp channel on the 8th of April and to date it still hasn't been actioned upon. I've tried calling them on numerous occasions, only to be on hold for long periods of time.

The tracker that they had installed back in 2013 has no longer operational since around 2017. I no longer use their services, yet I still get billed on a monthly basis.

Here's the reference for the cancellation request: CAS-***-Q8W2

Please cancel my contract!