SIP / DID providers anyone?

Apologies if some of my question seem a bit stupid but I’m pretty new to VOIP.
I have a problem with a SIP / DID provider that is giving us an unreliable service (dropped calls and regular downtime). I need to find a replacement provider. From what I can tell we have just over 60 DID’s and 14 channels. I’ve been educating myself as much as possible on the subject and what I think I need is an SIP trunking provider willing to port the existing DID’s to their service.
If anyone could correct me if I’m wrong and also recommend any DID / SIP providers that are 100% reliable.