That still doesn't mean you spend zero on average. I assume pretty much all your clothes are less than ten years old. To have a 3.5€/year average, all the clothes you own would need to have costed at most 35€ total, which is clearly unrealistic.

Though 35€/year maybe is achievable, especially if you get/wear shirts, hoodies, maybe even shoes from conferences or company events.

You probably at least still need a decent pair of shoes, one set of nice clothes, a jacket, pants, and underwear. 350€ to get that stuff for ten years still sounds very tight but maybe possible.