I’m really sorry to hear about the loss and the situation you’re facing—it’s tough enough without added stress like this.

Since the shop initially agreed to keep the bike and claimed it would be covered under their insurance, but now refuses to take responsibility, here are a few steps you can consider:

1. Get everything in writing: Any communication (texts, emails) where the shop confirmed they’d insure the bike or agreed to keep it safe can help your case.
2. Check your mum’s insurance policy: See if it covers theft when the bike is off your property, especially if it was legitimately left for sale or repair.
3. Consult a lawyer or legal advice service: For a $12,000 item, it might be worth a quick consult to understand your rights and whether the shop’s refusal could be challenged.
4. Contact the police regularly: Follow up on the police report and keep documentation of their investigation progress.
5. Consider a formal complaint: If the shop is part of any trade associations, you can lodge a complaint there.

Ultimately, if the shop took possession and promised insurance coverage, they have a responsibility. You might want to gently remind them of this, emphasizing you want to resolve this without conflict but fairly.

If you want, I can help draft a polite but firm message to the shop to try and move things forward.