ALDI TALK offers EU-wide unlimited calls & SMS with 60 GB of data for 69.99 EUR per year. That is 5.80 EUR per month for unlimited calls/SMS and 5 GB of data [0]. I switched last year from O2 (they use the same network) after I realized that I only used more than 3 GB of data in two months during the last 3 years. I essentially cut my mobile phone costs by 70% for the same service. Compare to the O2 bloatware, the ALDI web interface is lightweight, fast and simple.

For 8.25 EUR/month, you get 250 GB of data per year, and for 12.40 EUR 450 GB/year.

[0] https://www.alditalk.de/jahres-paket