Start by working out which of these you have.
Bait disappearing, trap not sprung. You are using too much. A pea-sized amount, pressed firmly into the trigger pedal or smeared just underneath it, so the rat has to work at it rather than lick it off the surface. A generous smear lets it feed from the edge without ever putting weight on the pedal.
Bait untouched. With rats, the commonest answer is simply that they haven't approached yet - they are neophobic, wary of anything new on their runs, and often take several days. Leave traps in place rather than moving them around. Beyond that: too few traps, wrong placement (tight to the wall, at right angles, trigger end nearest the skirting, where you have found droppings), or your scent on the trap, so wear gloves. If nothing changes, leave traps baited but unset for two or three nights so the rats feed confidently, then set them all on the same night.
If placement and baiting are both right and a week still gives nothing, question the target rather than the method. Old droppings look much like fresh ones, so the activity may have moved on or already stopped - trap where you are finding fresh droppings, not where you first heard something. And scratching overhead isn't always rats; squirrels and birds in a loft sound very similar and won't go near a rat trap.