No worries, welcome to the club, and you'd be a lucky guy if you'd faced a different scenario.
Well, when I'm flying westbound VECF has never replied to my calls on HF, only on VHF -- but 10 minutes before its FIR boundary (when leaving VGFR Airspace). So, while in the Yangon airspace I always try to contact Dhaka as soon as possible (most of the time more than 10 min before its FIR) while on CPDLC with VYYF and keep watching the IFBP frequency (and 121.5 as well)
As far as I know, based on my experience in that area, Dhaka and Yangon VHF frequencies work well. BUT I've never requested FL changes before leaving that mess.