I filed an amended return to the IRS. However, I found out I don’t want to file the return. What number at the IRS should I call to cancel the amended return?

[macuser_22]

None.   Once an amended return is mailed (or e-filed and accepted) , there is no way to cancel it.

[Critter-3]

There is no way to stop a return once it is filed ... so if you efiled or mailed the amended return already and needs to be corrected again it will need to be amended again but only once the first amendment has fully processed.   

[macuser_22]

And it takes 4-6 months to process an amended return.   If you file a 2nd amended return before the first is fully processed and have two returns in the system at the same time then expect up to a years delay.