I just got a new oxygen sensor & catalytic converter so why does the check engine light still turn back on?

My car ped the California smog check after I got a new catalytic converter 9 months ago. Fast forward to now...I moved to Texas. Damn check engine light came on. Went to a shop & they read 2 codes. 1 was for the oxygen sensor. 2 was for the catalytic converter. Got a new oxygen sensor & a new catalytic converter. Drove less than 30 miles before the damn check engine light came on again. Gotta get a Texas state inspection. What do I gotta do to p it? Please help!