You need to poison mice effectively!! To be effective you need to put down a lot of poison in a lot of places, mice are sporadic feeders and will only nibble a little bit in each place, so unless there is a lot of poison in a lot of places your mice will just feed off it without taking a lethal dose. You will need to use a specific "mouse killer" and not a rat/mouse killer, they are useless. Rats are a walk in the park compared to mice, rats will kill off so easily but mice are very different.
(Pest Controller for 13 years)