When my kids started fighting sleep at night the only solution we found that worked was dropping their day sleep. Then they went back sleeping really well at night and settling well.
Is your DS still having an afternoon sleep?
Exactly what I was going to say. DS went through a stage of getting out of bed multiple times and wouldn't go down for hours (sometimes as late as 10-11 - and we go to bed before that!). Since we dropped his day sleep for good not long after he turned 2, we haven't had this problem anymore. Bed by 7.30 here!