I suppose some might be so incredibly bad at their job that they don’t have staff for constituent services, but most do. They don’t tend to ask who you voted for before helping. I’m in a very red state, vote for democrats, and have had state and federal republican rep offices help me out several times.
I am a very conservative person, but I've lived in deep red districts and deep blue ones, and I've honestly never had a problem with any. If anything, I've noticed that the representatives I complain to a lot want to help more because they think they can get another voter by simply being decent. That's if the rep even gets involved.
This is it. Calling your representative almost never results in you actually directly communicating with your representative (for better or worse). You will always get their staffers, who may have completely different moral and political agendas.