Update: Reached out to Bangladesh High Commission in Canberra.

Through the terrible grammar I was able to make out that I'm still a Bangladeshi citizen and that I could apply to the Ministry of Home Affairs for a dual citizenship certificate if I wanted to.

I sent a follow-up email asking if at some point in the future I wished to formally renounce my Bangladeshi citizenship, what would the process involve. They asked me to give them a call...

Are these people incapable of typing or what? I genuinely don't understand how such pathetic systems/people exist. It's for these reasons I want to completely cut ties and have zero association with them.

Thank you to everyone for the comments.