|are like up in Canada. In the US, I believe shops can put liens on titles for non-payment. If it's similar in Canada, the OP might end up in a much messier position as compared to paying them and pursuing reimbursement in court.
To the OP - did the shop not do a baseline pull before they started tuning? I'd imagine that usually would be step #1, and if they did, it would have been obvious if their tune degraded performance, or if their dyno was just reading wrong.
As much as it sucks, I'd 2nd figuring out a way to get your car back (unbricked), get it tuned properly and documented, and then pursue reimbursement after the fact.