FBA has the worst customer service

I have shipped to Amazon FBA back in 2023 and the items i shipped were lost. Then amazon account managers reached out and covienced me to ship FBA again, it's easier, less fees, and it provides better service to clients. Which I am all in for. I shipped again samples to FBA and get again they are lost. I am working now to make up for losses that Amazon is causing to me. I have opened tons of cases with zero support and when I call customer support, {Moderator Edit: personal data} got mad at me and said I will hang up because I told him I am not happy with all these delays and you're not giving me a time frame of when you can resolve this issue.