You can say it either way. The 'with' variant emphasizes that you're 'with' a group, organization, company, etc. But you can also say that you're 'from' the organization... 'with' just might sound slightly nicer, i.e. more of a polished customer service sound to it.

"With" establishes a symmetric connection. Austin is connected WITH the shop as an employee. The shop is connected with Austin too. That is SYMMETRY. "From" establishes an asymmetric connection. The authority that gives Austin a reason to talk to you comes FROM his employer (the shop). However, the shop is not FROM Austin. That is ASYMMETRY. Similarly, you might be FROM Spain in the sense that you are its citizen.