Ann Emmert Abbott
Of course your writing creations are covered by copyright law, whether they were performed or not, unless you signed away some or all your rights. It sounds like you didn’t.
Taping and producing DVDs enters a murky area if someone else did that work, but you still own the copyright to your creations and thereby control copies of it, including derivatives.
I’m very fond of using professionals, especially when money is involved. Get yourself a good IP (Intellectual Property) attorney, preferrably one familiar with your field. It may be that something as simple as a letter from an attorney will settle the issue and smooth ruffled feathers.