Just a bit of devils advocate here. First the owness in the situation lies on your instructor and the dive shop. If you have done EVERYTHIng you needed to do. Filled out all the forms, completed all the Knowledge reviews, quizes and the test, paid for the course, provided pictures for the certification card and had your student recaord file and log book properly signed and filled out. then there is no reason your card should be held up.
I am a PADI instructor and in addition to all the other paperwork I have to keep track of I need to keep a "HIT" log...this is a log of all my students who owe me something... a make-up test, thier knowledge reviews, payment, etc... So i can justify not sending the the paperworkto them and PADI... I currently have 15 divers on that list. I directly certified 76 divers last year and assited in the training of at least another 30... so I am looking at roughly a 15% non-cert for some reason beyond my control ratio.....
Now I am not saying this applies to you or your situation, becuase i know there are people in the industry who fail to do what they are supposed to do.
My advice to you is to go down to your dive center and meet face to face with the shop owner and the instructor and get this settled....a phone call or an e.mail doesn't ever seem to get the right message across to someone who owes you something.
Plus if there is indeed a lack of performance issue you can fill out a quality assurance form on the instructor with PADI and PADI must address the issue and discipline the instructor as necessary.
Lastly if you enjoyed diving don't let this butt-head take that away from you