When you have an excellent idea, you can be sure there will be others looking for ways to copy it. Some might take inspiration from it, others might take it and adapt it, others, the lazier, less creative ones, will steal it outright and use it as it is.
When it comes to your intellectual property, if you want to protect it, you need to be proactive. Putting patents in place in one such form. Yet, despite that patent, you should still expect others to try and steal it and be looking out for anyone who does. If you think someone has used your design, then what?
Did they breach your patent?
The first thing to do is check to make sure that you actually patented your product. If you have only ever taken out one patent, then you probably know, but if you are part of a bigger team, constantly coming up with designs, some of which you patent and some of which you do not, it is easy to get confused about what is and is not protected. Or perhaps you patented an earlier version of a product, and what the other company has copied relates more to a later iteration. Is that covered?
Was it intentional?
Have you ever been in a room with someone and you both say the same thing at the same time? We do not live in isolation, so if you had an idea for something, it is entirely possible someone else had the same or a similar idea without ever having met you or knowing you had thought of it.
What harm have they done you?
Has someone taken your toy idea and mass-produced it in time for Christmas, selling millions? Or have they used it in a minor way, or are only getting started on their plan to exploit it?
What solution do you want?
Do you want an apology and for the other party to cease? Or do you want them to pay you a financial penalty? In some cases, you could even decide to co-operate to help your product reach further than you could alone.
To understand what you should do, first, you need to understand more about patent law and how it applies to your particular situation. Experienced guidance can help.