Gave heed (proseichon). Imperfect active as in Act 8:10, Act 8:11, there with dative of the person (autōi), here with the dative of the thing (tois legomenois). There is an ellipse of noun (mind). They kept on giving heed or holding the mind on the things said by Philip, spell-bound, in a word.
When they heard (en tōi akouein autous). Favourite Lukan idiom, en and the locative case of the articlar infinitive with the accusative of general reference “in the hearing as to them.”
Which he did (ha epoiei). Imperfect active again, which he kept on doing from time to time. Philip wrought real miracles which upset the schemes of Simon Magus.