I had an issue with low volume on these headphones when I got them. I think I may have found a solution, it may help you too.
Try the following, when connecting your device to your source(laptop/phone) put the volume very low on the source first. Connect the headphones, it can be over Bluetooth (no issues), then turn the volume up to max on the headphones (while the audio source volume is still set low). Thereafter adjust the volume from your source. You would be able to get way more volume out. If its still not loud, try turning the volume back down on the source to a very low volume, then put the headphones off and back on, after it has reconnected, turn the volume up to max on the headphones (while the audio source volume is still set low). Thereafter adjust the volume from your source.
I was able to get it really loud that way. Basically ensure you turn the volume up on your headphones first then start turning it up on the source.
I hope this helps anyone having simpler issues.