Rare case. Seeking opinions

My car has been in the franchise holder workshop for the past 4 years being repaired under OD claim. Initially requested for total loss but rejected and they approved repairs of about 50% of insured value + pending "to inspect" another 60%.
As the years go by, more parts are claimed. But few months ago, the insurers officially notify they won't entertain any further claim.
1. Repairs are still incomplete
2. Claims already exceed economic value. Potentially, I've to pay another 50% of insured value to complete.
3. Insurer can't issue further instructions
4. Workshop won't agree to total loss as they already spent money on completed repairs.

What's your suggestion?

PS: no fraudulent activities as they are official distributor of premium brand for >50yr. For this rare model, parts take 3-6 months to import.