I can't think of anything that eats rose roots, well, not to that extent. Were they bare-root stock or potted plants you bought?

Would vine weevil eat rose roots?

Unusual for vine weevil to do that much damage in the ground, although, of course, they're present. The soil contains so many buffers, including natural predators, to disease and pest attack. Normally I would suspect rotting due to waterlogging or poor rootstock and perhaps the aftercare (without meaning to cast doubt on the ability of the grower in this instance).

I would go with poor rootstock. I have many roses in my garden, majority were bought bare-root, some of them were ordered online, the ones which came from online purchase, had hardly any root system, but a thin stick. I still planted them in the hope that they will form strong root system in time, but also knowing they may not make it, as my suspicion went, they did not make it. But, don't take this as the only reason, there could be others as well. Hope you can resolve this problem soon.

Thank you for your reply's, after reading them all, I think that the answer is probably POOR ROOT STOCK. I bought them bare rooted from a sale. I suppose you get what you pay for. Thanks to all who replied.
regards Michael Dean