Rear brake pad worn

Hi there!

Another rear brake issue / problem (in norway)

My twizy is 3,5 months and has travelled 2300 km. / 1400 miles. A scraping noise from the rear turned out to be the inner brake pad totally worn down, metal against metal; the outer brake pad not worn. Both sides. Dont use the brakes much, but occasionally brake hard.
The renault dealer just replaced the pads and said the guiding pins worked fine.
Not inspected the front. Have not yet installed the stainless pistons i have.

This cant be normal; i suspect it will be the same in a couple of months. Caliper problem? Or just wash it more often.
Planning to switch pads from side to side after a while.

It could be the handbrake not coming off fully. Happened to me.

Check both sides, Put he handbrake on. Note where the rear level is compared to the stop. There will be a gap of 4mm- 10mm take handbrake off and see if the arm on the rear caliper has returned to the stop. No gap arm is vertical and against the stop.

If sticking, Spray with some lubricant and work the level manually until it becomes free and then oil it well and keep checking.

A small gap on one side, the other seems ok. So it cant be the only reason. Thanks anyway!
Do other owners experience even brake pad wear?