Weird sounds when calling someone

My phone has been making these weird alien sounds and ending my calls for the last months. It’s been a hassle to make long calls because it always gets disrupted. Often times, I can’t receive calls either! I’ve been in contact with my operator several times and they can’t seem to find the issue, so I’m pretty sure it’s my phone’s fault. So, why is it doing this and how can I make it stop?? I have a video recording of the sound they make but I’m unable to post it here.