volume control issue

Hi everybody!
so i have some issues with volume control on my Z10.
yesterday, i was listening to music with spotify's app, the phone was connected to a bluetooth speaker. while listening, i was checking things on internet (with the phone too) and suddently the sound increase to the max, i wanted to low it it by pressing the volume button, but it was impossible. le volume was like stuck! i have noticed it sometimes happen when i'm on youtube. another thing, when i listen to music, always on spotify, with my earphone, sometimes the sound stop, i have to press play to have it back, sometimes the sound stop and assistant start, i don't know why, like if i have pressed on the middle button. i thought it was my case, so i take it off, but i have the same issues.
can someone tell me what happen with my z10? and what can i do to fix it please, it is very anoying