If you haven't seen the commercials ... Virgin Mobile's new ad campaign is built entirely around a fake Hollywood couple called "Sparah" -- a mashup of the names Spencer and Sarah -- and Pratt is pissed he and Heidi have become the target of a national joke ... with no paycheck to show for it.
According to Spencer, Speidi's getting ripped off -- telling us, "They should being paying for using our likeness. It's obvious they are trying to be us."
Pratt doesn't stop there -- adding, he and Heidi "hate" Sparah ... "It's nuts how much [Virgin is] promoting them, when they are obviously copying us."
Attempts to reach Virgin's celeb couple were unsuccessful -- but we're guessing ... "Sparah has no comment."