Tesco Credit Card

i paid online, full balance as i always do.
somehow the payment never went through..i must have clicked cancel instead of confirm.
first i knew of it was the late payment charge and big interest charge on my next statement.
i called to fix the problem, they were very rude, the card was stopped, i offered to pay the whole full balance as of that day, but as i had been penalised already, i would make the payment when it was next due. this was not good enough, they wanted a payment now, or the card will remain stopped
i have never made a late payment before, always paying the full balance.
apparantly i should have had a letter when the payment was missed, this never arrived, consequenltly i have been stiffed for interest.
after cancelling the card and paying the balance in full, i have been advised that i will get a bill next month for 'residual interest'
bloody cheek, i have written a letter of complaint.
they have lost a good customer today, look out sainsburys here i come...looks like it nectar points form now on.