Next time, tell them that the Union Minister of State for Electronics and IT has said that people shouldn’t give their phone numbers at retailers if there’s no justifiable reason. [1]
If they refuse to give an invoice, tell them you’ll report them for GST evasion. [2]
[1]: https://www.onmanorama.com/news/india/2023/02/13/rajeev-chan...
[2]: https://theprint.in/economy/govt-launches-gst-reward-scheme-...