Photoshop Elements 2018 without Serial Number

I purchased Photoshop Elements 2018 from Microsoft Store (MS) on 28th Nov 2017. It was auto-downloaded/installed and the software runs ok. I received an email purchase confirmation from MS but no Serial Number. I have repeatedly asked for the Serial Number from Microsoft Store (MS) through Store Sales, Accounts & Billings and Tech Support.  All state that they cannot provide a Serial Number and say I must obtain this from Adobe.  Adobe insist that I have to obtain the Serial Number from the retailer (Microsoft Store). I agree with Adobe.

I would like to register the product with Adobe as I have done in the past with my older versions of  Photoshop to obtain updates, tech support and possibly a future upgrade.

MS say that they can provide Tech Support but I may need expert knowledge based support and most definitely timely updates.

How can Adobe allow Microsoft Store to sell / download their software with no Serial Number as legal proof of licenced use?