Home office sent me a letter saying that I did not attend my biometric appointment

[shenkhorhui]

Good afternoon. I have few questions regarding my following situation

Basically what happened was:
5/8: I lost my BRP (Tier 2 Working Visa)
11/8: Applied for replacement BRP
31/8: Went for Biometric Appointment
31/10 (After 8 weeks from the BRP appointment date): Got letter from Home Office saying that I did not attend
1/11: Wrote a letter telling them I did attend
4/11: Called Home Office, they escalated the issue for me
10/1/2020: Need to go back to Malaysia

I wanted to apply for priority service, but according to the Home Office Website, there is a high demand for appointment, so I wouldn't want to take the risk to pay for the priority service and not getting an appointment.

My queries are:
1) As it is not a new BRP will they still send me a decision making letter or will they send the new BRP to me straightaway?
2) Is their escalation process efficient?
3) If I go back to Malaysia before I get back my BRP, can I apply for a single use replacement visa to come back into the UK?