It is very risky so do not rush. What will be the value of your accounts and funds, what if they both never get back to you and they only benefit? So the suggestion is correct to first contact the exchange support what to do to fix whatever happened to the accounts.
the negative trusts he has say nothing about this particular service, they are about account selling, so that's irrelevant. his idea is not clear but what I understand is that he means if an account is blocked or funds frozen due to KYC (coz that's the major reason of these cases) they can help with kyc and withdraw funds.
What kind of process will they do when it comes to KYC? Will they use their own Identity to access your account. Or will the owner himself submit their identifications using your account?