Procedure to cancel new connection contract

I had applied for a DSL connection and I had got a technician appointment on 5th August 2021. The technician did not turn up the entire day. Since then, I have spoken to o2 customer care 4 times to reschedule an appointment and I have received no response confirming a new appointment. I am tired of this kind of service. I want to cancel my contract (My contract can be cancelled any time).

1. I would like to know what the procedure is.
2. How do they take back their homebox router? Any advice would be greatly appreciated.