I wish you success. I had the opposite challenge, I had plenty of real world experience with process statistics but not in medical device. It was not until I had job experience with one med device manufacturer that other companies would give me a job interview. But enough about me, back to your question:
I offer one explanation. The potential employee doesn't want to hire a personal capable of learning or qualified for doing, they want a new hire who can go immediately to work with a minimum of coaching. I suggest there are certification courses in SPC where you can actually develop and perform SPC. The alternative of a book or video training on SPC does not provide a certificate. I encourage you to take a course that includes analysis of a real world problem with a real world client, because working with people to create an ordered project from scratch is different from a textbook problem. Sometimes the university will connect students with short-term internships, even if you work with no pay. Your local chapter of ASQ or engineering society would be another resource to find a client who could accept your free assistance in return for a letter of recommendation. That hands-on experience is what, I suspect, the potential employer is asking for from you.
Certification in process validation is not as readily available, but taking my idea one step further, you might enroll in a black belt program (which is sometimes offered through a university or ASQ) and if that project includes process validation, that would be certification that you have experience. I did a black-belt project for a non-profit organization and they were happy for my help. And, when you are asked in an interview about your real-world experience, you will have convincing real-world stories to relate to the interviewer.
