I thought nunca was supposed to go before the main verb?!! That's what duo told me in correcting another wrong answer of mine!!
Did you use nunca and no in front of the verb? I used nunca hablan and it was accepted.
Why can't it be "Esos señores ingleses no hablan nunca español"?
Creo que sería mejor usar el sustantivo Castellano en lugar de Español, porque España tiene otros idiomas.