@Hy81 , Welcome to the Community!
We have checked your bill and found no error.
We would be happy to explain your invoice to you.
1. your invoice includes a pro rata settlement for February (6.2.2020 to 29.02.2020), as well as the whole month of March
2. the pro rata settlement of February was performed because the product was changed the 06.02.2020
3. you are welcome to calculate March once. That would be CHF 69 for your entertainment product and CHF 15 for the Premium Plus. That makes a total of CHF 84.
Thus the statement of the employee in the chat is correct.

If you have any further questions, we are at your disposal.
Greetings
Daniele