You might have scored a backplate with burred slots - I had a Halcyon plate like this, and it chewed up my webbing in one of the slots. Simple solution is to go to a hardware store and spend $3 on a circular file used for sharpening chainsaw blades - it fits in the slots perfectly, and once you've removed all of the webbing, just touch up each slot to remove any burrs. I think emery paper would work just as well and be cheaper, but the file was something I had lying around.
Reef Scuba sell replacement webbing, I just changed mine after 18 months of use - not because it was frayed, but because changing from a wetsuit to a drysuit left it a little short. The webbing is super strong, and I wasn't going to replace it until it was cut through at least a quarter of the way. It's pretty cheap, and depending on your size and exposure protection, you'll want around 11-14 feet of it, 14 feet should give you *plenty* of slack to play with.