Several things it could be.

Did you see the pads that needed changing? did they need changing or was it a fitter on upselling bonus doing his best? were decent quality aftermarket pads used, ie Brembo Apex, if OE pads were used i suggest trying Brembo pads (and discs if required) next time, lasting much longer plus improved braking over OE products on the family Aygo....an overzealous fitter is my first choice here, usually by the time a second set of pads is needed the discs are getting a fair old wear ridge but you don't mention new discs being recommended, its easy for you as a punter to see how good or bad your own discs are, not quite so simple to check pad depth remaining even if you know what you are looking for via a small mirror.

Have the brakes been serviced properly, i don't mean has some bod peered at them and sprayed brake cleaner about, they might need a proper strip clean and lube up (seldom usual service regime at many garages, where peer/brake cleaner is typical), make sure the rears are included in this because whilst they don't contribute much braking effort they aid braking and stability...a clue to sticking or seizing calipers/sliders would be hot brakes for no good reason.

Does lack of use allow the discs to rust up and pit, also after washing the car do you drive it a little way to dry them up before parking up so the discs have a better chance of not rusting up, if the discs get pitted they will wear pads quickly.

How and where do you drive, do you leave braking late, do you not flow onto moving junctions keeping the vehicle moving or do you come to a full stop when not needed or rapid stops regularly, no criticism intended lots of people don't realise their driving isn't smooth or too harsh.

For clues to driving issues look at your front wheels (or inside the trims if you have steel wheels), are they covered in thick brake dust, if so clean them properly then try looking and planning further ahead for a few hundred miles and see if it's improved the brake dust issue.

Edited by gordonbennet on 17/05/2020 at 07:59

Can't guess whether being an automatic would make a serious difference, but I would have thought not much. These days, post-asbestos, pads and discs tend to wear at similar rates, so it's funny that the OP has not been fleeced for discs as well. Unless there has been a misalignment somewhere, perhaps.

IMHO no car should need new pads that often, even with heavy braking. It only needs so much effort to stop a given car from a given speed, heavy or light.