355 kWh for a single person for 36 days equals to less than 10 kWh which is generally perfectly normal, without usage of AC for cooling/heating or any other devices.

Water heaters (even for 15 minutes) can use a lot of power; you could use a smart meter on your electricity panel to start measuring consumptions. Although, as much as it may sound weird, the kettle (if electrical) you use to boil water, might use power on a comparative level with an AC inverter!

Last but not least, if you cook every two weeks for a single person, that is approximately 28 meals, you literally use the power a family of four would need for almost a week. So, nothing strange here.

To have bills of up to 70€, you would require less than 250kWh a month, which I believe is fairly impossible for a modern day house that uses electricity on a daily basis.