Someone talk me through getting rid of german cockroaches?

Stop spraying. Spray scatters them into the walls and they're back in a fortnight. Gel bait (the fipronil or indoxacarb ones) in pea-sized dots along the back edges of cupboards, under the sink, behind the fridge and cooker, under the kickboards. Diatomaceous earth puffed into the voids as well. Then starve them: no dishes left overnight, bin out, hob wiped, sink dry. You'll see more for a few days as they come out for the bait, that's normal. Re-dot after two weeks. German roaches breed fast enough that this is a four to six week job, not an afternoon.