Getting called by Virgin Media sales team several times a day but operator cannot hear me.

I've been getting calls several times a day from the Virgin Media sales team, and every time I pick up, no matter what speaker setting I have, nobody can seem to hear me. I can literally scream down the phone, put it on speaker, put my headphones in, and nothing. Just the operator going "Hello? Hello? Hello? Can I speak to [name]? Hello? Hello?". 

But of course this is also only from the sales team, as Virgin Media have failed to do anything about my ongoing issue with my emails which I've been trying to get a resolution for for over a month now. Please can somebody help me with BOTH of these issues as I'm absolutely exhausted dealing with a service that not only won't help me but is actively making my life more miserable by calling me over, and over, and over again just to say "Hello?" a bunch of times and hang up.