Quality of 'Offshore' Contractors

So this was my first client project with a new company, that leveraged 'offshore' developers to aid in the development efforts. First observations, offshore contractors introduced a much higher number of defects than company FTE's, most were less than active participants during sprint/epic/user story conf calls (unless called out by the SM/PM/EL), the majority of them were not accountable for their own code reviews, causing major delays in deploy-able product. Yes their billable rate was 50% of that of the FTE consultants and devs, however their output was close to 35% of the FTE dev team. Is this normal? How do you eliminate these problems mid-project when they do not listen/respond appropriately to EL/PM directives and client requests? (putting my flame suit on now) TIA.