not only ... but

[Susiest]

Dear Teacher,

I am a bit confused with the structure 'not only... but also/but ... as well.
As I understand there cannot be any negative forms before or after the "not only" structure, since it does already serve the negative form. EG: Not only did I forget to turn off the tap in the bathroom, but I left the door open as well. (if that is correct at all). However, if I want to ephasize a failed action, how do I use the the sam structure? EG. the prices didn't go down/ they went up ...??
Please help!
Thank you in advance
Susiest

[rlfwood]

Not only did the prices not go down, they went up.