Xps 13 9380 service tag not recognised by dell

Hi

I just purchased a Dell Xps 13 9380 from a 3th person and It has several problem as well as sound and sleep problem .I just started from update the BIOS and as soon as enter the service tag in Driver and download section in Dell.com it mentioned It is not recognized ,I am wandering how it is possible ,Is it fake version of this laptop .when I tried to update its BIOS version downloaded from Dell.com again failed .Please if somebody has same problem or one of Dell technician can help me . Thanks and appreciate .