I'm sure this isn't actually what happened, but when you said "as I have a loud voice" and then "did a few calls" and finally "shoulder shrugs at their end", I imagine you shouting over the phone to them, and them not understanding why your are shouting instead of just talking :P I'm sure it wasn't like that though, just what popped into my head.

Maybe this isn't any of my businesses, but couldn't you just talk less loudly, if this is such a issue? Most microphones are good enough, and were in the 90s too, to pick up normal conversational volume :)