Common wall issue to old neighbour and new neighbour

A common wall is made between my house which has 2 floors and neighbour househad only ground floor.The neighbour sell the house and gone somewhere else .ew neighbour is constructing a second floornow I contact old owner about half money of common wall he said I have sold house an you ask to new owner of that house now when I ask the new owner then he says I will not give you half money you talk to old owner house Both are saying no for the common wall money what should I do now