BTW, don't back down - if the customer wants to settle thats fine (obviously) but let them know that now the wheel's in motion they'll only stop once the bills paid. That means none of this "if you stop now I'll pay you next week" (they won't) - just say "sure, if you clear the bill next week thats fine but please be aware that until its paid, I can't stop the legal action".
Get on your invoice: "Title to the goods remain the property of (YOUR COMPANY NAME) until paid in full." which will mean you can take it back if they don't pay (no good in your case but without this legally you're knackered.
You can also charge interest on the amount owed - check google for statutory interest on monies owed...