Complaint about monitor service support exchange

I bought a DELL ULTRASHARP U2720QM, recently it is broken. And after self-checking according to official steps, I submitted a service ticket on official website. After discussing with the service support, they promise me to change a refurbished one. But after receiving the replacement, i find they give me S2421HN. It's so easily to find the replacement is far poor than my origin one, and the mistake is such low to let me this is purposed. During the whole process, i accepted many times calls to ask me when can i return the old one back. Btw, i received distribution information from DELL's official emails, and it says the System type is DELL ULTRASHARP U2720QM, so i believe in the dell's system it should consider to send me this model, but it is actually not. All the process i communicate through the whatsapp and emails, i can provide screenshot if necessary.