This is an M1014 barrel and has a FIXED MOD choke.
https://www.gunpartscorp.com/products/1439820
This is a commercial barrel with interchangeable chokes.
https://www.gunpartscorp.com/products/982970
If you are truly unhappy, you could simply come out of pocket and buy one of these, or you could ask Benelli to do it for you, or some voucher/reimbursement or some such maybe. That said, FUNCTIONALLY, your barrel is just fine, but aesthetically and so forth, I'd be frustrated like you seem to be.