Who keeps copies of knowledge reviews and tests? I don't think I have ever even been given copies in any course I have ever taken. I would think a receipt showing you paid for the course and a copy of the temporary card should be sufficient.
If you paid for the course with a credit card, you may also want to try disputing the charges. I have no idea if it would work, but it's worth a shot.
I'm not an instructor... but I've taken a few courses and am Nitrox certified.
You should have the book with the Knowledge Reviews in it. Standard is to make copies to turn in. As for the test....yea, nobody keeps that except the shop.
Now, lastly..... and not to be mean... but Nitrox is a "paper" only course. No dives are required to earn the certification. Optional dives are available... but not required. The "skill" for Nitrox would be checking your tank and then breathing underwater. Checking your tank is something you would do in class (with a meter).... so why make you do a dive?
It's possible that what the dive center did was a local class that covered the bases for diving safely with Nitrox but not certifying you. If the dive site was limited in depth and you were under supervision this would be a possibility. The primary danger with Nitrox is going too deep for your mix and having Oxygen Toxicity which results in convulsions. Convulsions underwater are contraindicated to living to tell about it. Again, I'm certified but not an instructor, so someone else might correct me if I've mis-spoken. Take that with a grain of salt.
You would have been trained on the Nitrox 32 and 36 tables and would have a set of RDPs for Nitrox.
So....
- did you get a green book about Nitrox from Padi?
- Did you learn to check the tank with a meter?
- Did you learn to use the Nitrox (or EAN) 32 /36 RDP?
- Did you take a PADI test and turn in copies of your Knowledge Reviews?
If yes then you probably took the PADI course.... if not then you took some other derivative and should consider going ahead and getting your cert. The class is reasonably easy, takes about 1 evening, and isn't that expensive from most dive shops. It builds on what you learned in OW.