Dell service tag not working

Hi there,

I have a brand new Dell Vostro 7620 which is about 2 months old and everything including warranty info was working fine.

Now my service tag is not being recognised by Dell's website or software in order to get an OS boot key which I want in order to upgrade SSD. 

I can sent a picture of the BIOS with the service tag if needed but I'm just not sure why it is no longer recognised and on dell recovery software it says service tag doesn't exist.

It is a similar issue to this person https://www.dell.com/community/Vostro/Service-tag-not-recognized/m-p/7913268 and I also bought via a reseller although it was first ever opened and used by me.

Any help would be very appreciated Thank you.

Khyran