The courses were at my own expense !
Paid for by Me
The original certificates are yours, then, and the company has no right to retain them. It needs copies for its own records, but the originals are your property and they must return them.
For anyone's benefit in the future, you should NEVER hand over an original certificate; a "Certified true copy" is entirely adequate for he company's records, and that can be done in the QA office, or hangar office, in accordance with company MOE procedures. For contractors, most QMs will accept certified copies signed by reputable agencies, but some require
sight of the originals on arrival, and then hand them back.
The certificate issuer will usually, and certainly should, issue a duplicate replacement on request, perhaps for a reasonable, small, admin and postage charge.