2 replacement AW3423DW sent back with proof, getting emails saying it wasn't delivered

Hey, this has been a very long process, of getting pretty much nowhere. I've contacted Dell 2 times now and opened 2 cases. I shipped out the replacement parts back to Dell on April 19th and it got delivered on April 23. I have both proof of delivery invoices to prove it. But every time I opened a case about this Dell always says "I will talk to my team about this and come back to you" and they never come back to me and help me resolve this major issue. Both parts cost almost $1000 and if I get billed for something that has been clearly delivered and I showed them it was delivered, I will be bankrupt. Someone please help me. Thank you.