Another vote for Telnyx, through if you have much traffic to rural landlines or ‘free’ conference lines, check their rate card. Most destinations are $0.005/min., some are $0.01, but a few are as high as $0.07. If used only for outbound, your MRC will be zero.
However, please describe the issues you have having; failover is a tough problem. For outbound, it’s trivial if the primary stops responding to qualify or loses registration. But if you’re having trouble with e.g. choppy voice, one-way audio or DTMF not passing, FreePBX won’t know to fail over.
Assuming that the system is in US or CA, failover for geographic DIDs can’t cover most failure modes, because there is no way to quickly change the assigned carrier for a number.
For toll-free, your resporg can set two carriers in the database, resulting in outstanding reliability, provided of course that the PBX is itself reliable and has redundant power and internet connectivity. Some providers such as VoIP Innovations do that standard, and most others who are their own resporgs will set it up for an outside secondary carrier.
As a primary provider, Telnyx offers many features. AFAIK, they are the only carrier that provides ANI on geographic numbers, SMS and MMS, and also allows sending an arbitrary caller ID.