Whilst it may "amount to the same thing", Plusnet was applying an explicit surcharge for card payments, NOT offering money off your phone calls or broadband if you agree to direct debit. I had to Google the date of the law change - it was January.
I wouldn't expect PN to exactly advertise that you can now pay how you like without being surcharged. They probably still push DD as the default, and hope not too many rail against it.
Edit: I should probably add, for the benefit of the original poster, that I'm NOT sure it's possible to manually pay every month.
My payments are still automatic - they're just charged to my credit card instead of DD. So in theory, just as open to the OP's worry about being mischarged/charged twice. I've never had it happen, though, and credit cards have protection against unauthorised charges, just as direct debit has.
Edited by TLM (Sat 15-Sep-18 19:58:08)