I had a similar issue on a Nokia 8 that I returned because of not finding a fix (this solution now reported to Nokia) and now the same presenting issue on my Nokia 7 plus.
If your bluetooth pairs with a speaker but you get no sound from the bluetooth speaker try the following:
In bluetooth menu, find the device in question, tap cogwheel and untick HD Audio: AAC. (device may need to be actively paired to see this?). Re-ticking this will cut off music too.
Brilliant....problem solved!! Thank you JazzUK777 :-)