It is possible that the product you received is expired or has been contaminated during the manufacturing process. The brown dots could be part of the natural ingredients, but the rotting garbage scent is not normal and could indicate that the product has gone bad.
As for the authenticity of the product, it is difficult to say for certain without more information. SomebyMi is a well-known skincare brand, but there are also counterfeit products circulating in the market. It's possible that the seller obtained the product from an unauthorized source, which could explain the quality issues.
If you are not satisfied with the product or have concerns about its safety, it's best to contact the seller and ask for a refund or exchange. You can also reach out to SomebyMi directly through their customer service channels to verify the authenticity of the product.