Discount on bills?

Hi

If i had a bill that had a credit involved, eg. a phone bill of $80, but phone company gave $3 credit.

I used to create the bill and then do another line allocated to same thing (phone), but with a -$3.

With the new update it won't let me put in a negative amount.

I tried making the bill for the whole amount and then recording a payment with a discount of $3.

This made the total correct, but the gst amount was then wrong.

how do i do it?

And how do I now cancel and delete the one i just tried, as it was wrong.

(it won't let me delete the recorded payment of $3 discount. Keeps coming up with an error).

argh..... I HATE all these changes!

Please help

thanks