Why can't telecom customers cancel their service without being billed for months afterward?

“I cancelled my mobile SIM plan last week and called to confirm the cancellation. However, a week later, they still charged me for the next month's…”

“I have moved houses and no longer require the service. I have spoken to them on the phone multiple times, and they keep calling me to ask why I’m leaving. Every single time, I tell them I’ve moved and want to cancel. Eve…”

“I have sent four follow-up emails in the last week alone demanding a simple cancellation confirmation email, and they are completely ignoring them. If you want a provider that provides a shaky connection and then holds y…”