Amazon Marked My Package as Delivered but It Has Not Arrived

The product I ordered from Amazon was not delivered, yet it shows as "delivered." Upon checking further, it appears to be "in transit." I've been waiting for the package for three weeks, and this delay has disrupted my plans. On what basis did the person who signed and approved it as "delivered" do so? I’ve called customer service, and they keep saying, "You will be contacted," but no one has called, followed up, or provided any information for days. The lack of communication and accountability from Amazon is highly disappointing. Despite being a Prime member, I’m facing this issue. I urgently request that this matter be resolved and my package delivered to me promptly.