No sim found in iPhone SE

Hi,

I have purchased Iphone SE with xfinity and activated, later I have placed an exchange for iphone 11.

Im yet to receive the iphone 11 as the model was not available in the store.

Now the sim in iphone SE is not working and I went to store and they gave me a new sim and asked helpline to get that activated as they are not able to activate in store,  now after sometime i called helpline to activate, however they are not able to activate. Now they have asked to go back to store.

They mentioned this is due to my exchange that I have made, however still I have not received

Now I m left without any number and running b/w store and helpline

Appreciate help on this