Totally confused on ISBNs

So, this book thing is a never ending education! 15 months ago we published our first book. Like a lot of first time authors it was easiest to just go with Amazon at first. Now, we’re ready to go wide.

I took what I thought was good advice and bought Bowker ISBNs for my print books. Now that I want to go wide through Draft2Digital, I’ve been informed that I can’t use the ISBN that I own, with them. Amazon is the only place it’s been used, and it was not signed up with wide distribution. Only KDP.

I thought that’s why you bought your own. I knew if I used the free one Amazon offers I wouldn’t be able to transfer it, but why can’t I use my own ISBN?

D2D says I would have to delist my book with Amazon (where I’ve spent lots of money on ads and building a following and start from scratch. Is this right? If it is, why should I buy Bowker’s expensive ISBN if all the platforms offer free ones.

Color me confused!