How to by pass SQL native error for duplicate records?

Question

I am getting this error when a program executing, when it is trying to update data in the table. Is this because of duplicate record ? what will be the condition to avoid sql error for duplicate record. below error:

Description = [IBM][CLI Driver][DB2/NT64] SQL0803N One or more values in the INSERT statement, UPDATE statement, or foreign key update caused by a DELETE statement are not valid because the primary key, unique constraint or unique index identified by "1" constrains table "FH.Product" from having duplicate values for the index key. SQLSTATE=23505 Code here:

 request = [
    UPDATE FH.product
    SET numchassis='%3',mtoc='%4'
    WHERE numchassis='%1' AND mtoc='%2'
]      
query=Constructed String(query,sChassis,sMTOC,sVin,sNewMTOC)
SQLChangeConnection(nCnx_DWH)
bRes = SQLExec(query,"REQUPD3")
IF NOT bRes THEN
    SQLInfoGene("REQUPD3")
    gsError=SQL. MyError+RC+Request
    sSQLState is a string = SQL. MyError
    sNativeErrorCode is a string = Spaceless(ExtractString(sSQLState,2,"Native Error Code ="))
    sSQLState = WithoutSpace(ExtractString(ExtractString(sSQLState,2,"SQL State ="),1,RC))
    //If update error because duplicate
    IF sNativeErrorCode = "-803" AND sSQLState = "23505" THEN
        Delete
        ECRIRE_TRACE("calling If condition ")
        deleteDepot(sChassis,sMTOC)
    OTHERWISE
        FIN_ERREUR()
    END
END

Problem is in IF condition, it is not calling the deleteDepot()method.