My prize from a company has not came in the mail yet! What should I do?

[A person]

On around February 20th, I saw a tweet on Twitter for a company, the company said that the first 5 people to send in a photo of a famous person would win a signed product by that famous person. I was the 5th person to do so, a few days went by and I emailed them and asked for confirmation that I was a winner, they did not get back to me by email, but rather on Twitter (they said "Hey, you won an autographed < companies product>! DM back your full name and shipping address and we'll send it. Thanks for participating!).

I sent my info to them right away. It's now March 19 and I've still not got my prize. I've messaged them 3 times (one message on Twitter and two on email) and they have not got back to me at all.

What should I do? Should I call them? Are they allowed to not give me the prize for some reason?

BTW, their Twitter account is verified, which means for sure it's their company account, so it's not someone making a fake prank account or something.

[Laugh it Off]

any account can get verified.
it was apparently a fake.