Amazon Partnered Carrier issues - Central Transport

Has anyone encountered issues with shipments consistently being held up by over 2 weeks with a particular Amazon Partnered Carrier? Our last 2 shipments have been assigned to Central Transport, and they pick up our shipment and then it gets held for weeks before they actually put it on a truck to transport it to the FBA warehouse.

I spoke with Central Transport and they said that they're backed up. If this is the case, I don't think they should be allowed to continue to accept shipments. It's unacceptable. I called Amazon to try and report the issue but they said there's no way to file a complaint about a carrier.

I don't want to ship to FBA with this company again. Any advice on using a non-partnered carrier is also appreciated.