Which contact form plugin is best for Enfold Theme?

Hi there,

so far we used the implemented contact form in the theme. It seems to work, but we have clients complaining about not being able to send us a message. If we try then, it is indeed not working. But it will again the next day or a couple hours later. I called the provider to check if there might be any issues, but they say it must be a problem with WordPress. Is there a plugin that can be used in addition in order to avoid this problem? It’s a doctors website and my client is not happy about her patients not being able to leave a message or an unreliable contact form performance.
I’d be glad, if you could help me fix this…

Best Katrin