Dedre Nielsen

As part of our incentive plan, the company provides annual shares which vest every 3 years. When the shares vested in July 2024 this amount was added to my payslip for the value of the shares at that time (34k). This amount has pushed my total taxable income over 100k according to my P60 and payslips, however I never actually sold the shares. The company is now going through some issues and those same shares, if I sold them today, would only be worth 9k. My question is what the right thing to do is here? My self assessment calculation shows I underpaid tax by 4k and now owe HMRC, but I've underpaid on money I never actually received? And if I remove the 34K from my income I fall back below the 100K mark. Please help.