I think it's highly unlikely that you will have failed your English Language GCSE if you got a good grade in the IGCSE.
But the short answer is that yes, you may put your IGCSE English down in place of the GCSE English Language. They are both equally valid.
The main difference is that IGCSEs are coursework-free (generally!) and so can be taken in one year, which tends to suit students in international schools better as they frequently move schools yearly.