It appears you are not taking anyone's advice. You should not have called the client's office - that's a big no-no. Since you've been nothing but paranoid about this job, why don't you just let it go?
Assuming this is about the same job as in your other threads, it's best to keep your questions in one place, rather than starting yet another post.
It's probably not a scam as such - I expect your client would pay you if you set the job up correctly, but the client does seem a bit dodgy in that he is using a company he is no longer with. If it were me, I would politely decline and move on.
I moved all your threads to this master thread as it appears that you were posting the same topic on a different thread everytime. Please be mindful of the Upwork Community Guidelines when posting on the community in the future.
You may report this client to the customer suppor team so that they can investigate it further. Please also follow the advise that Vladimir has shared above. I invite you to check these threads to help you work safely on the platform -
Working safely on Upwork:
Recently, we hosted an event with Upwork's Engineering Lead, Mike Maietta. In this event, we introduced this new tool, and Mike demonstrated how to use it and answered questions.Learn More
Upwork partnered Red Bay Coffee and artists commissioned from our own platform to bring the Wake and Make blend to life. We asked the creatives to share their freelancer journeys.Learn More
Virtual Talent Bench enables you to easily discover and connect with talent. Learn more about building custom lists of talent, adding tags, notes, and more to move your business forward.Learn More
Loom addition in messages provides more ways to easily communicate and share information on Upwork!Learn More