I need a valuation done to challenge a Loss adjusters overstated values

A Farm building one of six, built of timber frame and corr. sheeted wall and pitched roof had roof blown off plus other damage. The other five buildings some of which are about 100 years old some walls ,rubble and stone others rubble and some conc. blockwork all with Corr Iron roofing on timber. Very low spec. and outdated for farming nowadays. Insurance Assessors valued the total replacement at £90,000 +. they were insured for £28,000 + therefore 32% insured by their assessment.
The total 3497 sq. ft internal area of the six buildings and the damaged one 'A' is 1298 SF. = 37%. I have quotes to replace for approx £10,000. The INS company have this at £19,000. Can you assist me to challenge their position to at least change their
under-insured position from 32% to at least plus 75%. They are using £14/sf for framed and £24 /sf for solid walled build.