Ok chevy guys-96 vortec v8 5.7?

just had BOTH heads replaced. $2200 - month later acting up, spark plugs are so shot, not even funny. 8th cyl not firing. take it back to shop. now they say one of the fuel injectors completely clogged up, the rest(?) semi clogged. said they fixed it, now another $500+. is it me or #1 the spark plugs had to have been pulled the first time around to do the heads #2 while fixing the heads the fuel injectors wouldve been checked (since they were there) as well? they say no...i dont know, im just a girl. oh but they changed the oil and the fuel filter!