Aws “Advanced Consulting Partner” not professional, what to do?

We need an advice. We moved a huge setup from the datacenter of our client, to aws: we needed expertise from aws professionals to do it (due to our internal lack of knowledge in aws) so we did it in partnership with an official Aws "Advanced Consulting Partner". Well, migration is done (it took 2 months: pretty happy on aws tools, but prices a bit high) but we think the partner is unreliable and not professional: we think we are locked to them, too. We are thinking about strategies to solve the situation, probably by moving to another aws "Advanced Consulting Partner"... (the setup is pretty big and we lack of aws-knowledge so cannot everything without the help of aws experts) Any advice? How to choose a good aws-partner? maybe asking an auditing directly to aws on how the partner is doing?