You've most likely unknowingly disturbed the abs sensor wiring. There's a cable running down each strut to a sensor behind the hub.A while ago I changed the brushes in our washing machine motor and somehow managed to shear a wire on the motor speed sensor. I never did work out how I'd done it!!
the esp is part of the abs system - in short the esp controls the brake pressure to each wheel allowing the driver to avoid an accident under hard/heavy breaking much like abs does but at a higher level
The esp gets its information from each wheel via the abs sensor
Take off the front wheels (support the car safely - e.g. on axle stands) and have a good close look (with a good light) at the sensor wiring which runs to the back of each front hub. You will hopefully find a connector that you have accidentally dislodged.
Here's a picture from the workshop manual showing the cable routing that may help: