Thanks for all your contributions to this post. As the owner of said belts (and fingers holding belts in close up photos) It falls on me to report back and wind this strand up.
Having returned the belts for inspection to the supplier (and in the meantime re-fitting new belts purchased from Bongo shop) I received a full refund and refund for postage to send the damaged belts back.
No further explanation has been offered but hopefully a quality control problem may have been picked up. Based on the customer service received I would still purchase from auto jap spares again aka Mazda Bongo shop (as I have in the past). In these hard times we all need to shop around and get keen prices, but also need quality when it matters. The ability to put something right when it goes wrong is the sign of a good company.
Cheers
Spenner