I received a duplicate product a week after receiving the one I paid for. The company is a non-Jewish company in Utah. They would not know I am Jewish. They have not asked for the duplicate product back. Am I obligated to let them know and try to send it back? The product is a mattress that costs $1300.
Once you received the product you ordered and paid for, the transaction is complete. The second mattress they sent you still belongs to them, but it is like a lost object. Ein chiyuv hashovas aveidoh lenochri.
If you can create a kiddush Hashem by notifying them of its whereabouts, you should do so lekadesh shem shomayim. You are not required to spend time and energy to return the mattress, but if you notify them, they may arrange to have it picked up.
It can also be viewed as a mistake made by the company for the transaction you ordered. The halochoh is the same. As long as you did not cause the company to err, taus nochri muteres.
אין חיוב להודיע לחברה על הטעות אבל יש מצוה להודיעם לקדש שם שמים.
במדה ולא תחזיר המזרון, עדיין הוא שייך לחברה. אם לא עומדים על כך ששלחו בטעות, מותר להשתמש בו.
I was able to detect that you were Jewish from your name and email address. It is possible that others would be able to do the same.
The Be’er Hagolah on Shulchan Aruch (C.M. 348:5) points out that even in cases in which it is permissible to keep money that was gained through taus nochri, those people have not been successful with those assets. On the other hand, those that acted to create a kiddush Hashem have had great success in their finances.
There is also the possbility that at some point the company will realize their mistake and request that you return the mattress or its value. At that stage there is a potential chillul Hashem.