I have an iPhone XR paired to my hearing aids. Recently the phone started dialing random phone numbers or internet searches and it seems that the phone is being directed by the hearing aids. I wear a face mask frequently (Covid requirement) and I assumed that the interaction between the mask loops and the hearing aid triggers the hearing aid. I am very careful when I put the mask on and have even removed the hearing aids when I wear the mask. Ive disabled Siri because the hearing aids triggered her frequently. Despite being careful the problem continues and now happens even when not wearing a mask. I get a message on my phone “voice Control” and an announcement that it is dialing a number. Today I put my hearing aids into flight mode because this issue is causing me a lot of distress,
Call Ghostbusters. 
Seriously, this is very odd. Maybe somebody else has some ideas, but I’d go to an Apple Store.
What if you disable the tap control for voice assistant entirely? When I had my demo pair, since I never use voice assistant, I had both right and left sides set to the pause/play function.
Thanks for the response. I have now disabled tap control and that has stopped the spontaneous dialing of numbers
Great to hear! (Or not hear, in your case)
Don’t hold me to this because I’m not certain, but even though the app has the 3 gentle, default, firm tap settings, I THINK the audiologist is able to change or program what the default sensitivity setting is. Perhaps if he or she can significantly decrease the sensitivity, you can regain function of voice assistant without the hassle you have been experiencing.