Consider whether you wish to contact the author (sellers of items) whom you think might be breaching your intellectual property. There may be a misunderstanding that you and the author might be able to sort out without resorting to the formal processes outlined below.
In any case, consider keeping screenshots of any activity that concerns you so you’ve got the details recorded.

There are two main ways to let us know if you think your content is being used without permission:

for copyright owners – take action;
for other IPR owners, including trademark owners – the general IPR notice process.