All TV's have identification plates adhered to the rear of the set, if your doesnt then for some reason its either fallen off ("very" unusual!) or someone has pulled it off for some unknown reason, the "serial" number being essential for service purely as a measure against fraudulent service claims, i.e:- to stop a person claiming for another or second TV set and not the one that was originally covered by the warranty, the serial number of it being known.
By the way a company (any) cannot tell you what the serial number was on any of the products they have manufactured, as its not stored.
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