My father had told me not to attend that meeting, but I went anyway.
Literal
Father [topic-は] me [to-に] that meeting [to-に] attend-not [so that-ように] saying was [but-が], I [topic-は] attended.
言っていたが indicates the father's prior and ongoing instruction, contrasted with the speaker's disobedience. ~ないように言う (tell not to) combines with ~が (but).