We use the past continuous together with the past simple when past continuous describes a longer action or situation, and the past simple describes the action or an event. So when you say When I met him, he said he was working for a big company actually means that you met him (past simple interrupts the 'situation' described by the past continuous tense), and he was working at that time (longer action). I think you should use past progressive ( was or were + verb-ing ) in your example.
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