They have taken your work. The bad news is you worked for nothing. The good news is it won't hurt your UW track record because there was no contract.
As a brand-new UW freelancer, any invitations you receive are likely to be scam artists or people looking to take advantage of your inexperience and eagerness to land projects. There's always an exception that proves the rule, but be very wary of invitations until you establish a track record.
*Unsolicited advice alert* -- Spend some time searching freelancers to find ones doing the kind of work you want to do, who have credentials/skills comparable to yours. They are your competition. Pick out successful ones and study their profiles to see how they position themselves and what they are charging. Also, if you haven't already, take the time to become thoroughly familiar with UW's Terms of Service and with the mechanics of the platform: how proposals lead to interviews, how interviews lead to contracts, the different types of contracts, how to get paid, etc. And browse this forum, where you'll find a wealth of information and insight.
Freelancing is an uphill battle when you start out. You need a thick skin, the ability to not get discouraged easily, and a willingness to constantly adapt and learn from your mistakes (and your successes!).
You're not likely to get paid for the work you've already done, since there was no contract.
However, since they didn't pay you for it, you still own the copyrights, and they aren't legally allowed to use your work in any way unless payment has been rendered. If they do, you can easily send a DMCA notice.
Might be helpful to (politely) remind them of that.