I could find nothing in the medical literature showing Botox helps with acne scarring. Nor does it make biologic sense.
You might be confusing the use of Botox for acne scarring with its possible use for acne found in a relatively recent study. In the September 2008 issue of the the Journal Drugs in Dermatology Anil Shah claimed success in 17 of 20 patients when using Botox for acne. He felt that Botox improved acne in two ways: By blocking acetylcholine, sebum (oil) production dropped and the paralysis of the tiny muscles around the pores ( arrectores pilorum) caused the pores to become tighter. The problem with the study was that it was not blinded at all and was a small study. However, the results are interesting, especially in regards to the shrinkage of pore size. Anecdotally, some of my patients have noticed an improvement in their acne following Botox injections.
Theere are two broad classifications of acne scarring: Hypertrophic and hypotrophic. Hypertrophic scars are raised, usually due to an excess of collagen. Hypertrophic, which are more common, results in depressions in the skin: pockmarks, ice pick scars, box car scars, valley scars etc. A third type of "scarring", hyper-pigmentation, is sometimes thought to be scarring, usually by darker-skinned patients, but is not. We see that scarring is basically a problem of collagen, either too much (hypertrophic) or too little ( its destruction in hyypoplastic scarring). Botox would do nothing to correct this problem.
Further, what if it worked, for either acne treatment or scarring. Injections too deep, might hit the rather superficial facial muscle of the face causing sagging...just what you do not want! Also, would the scars return after 3-4 months?
You would best to see a dermatologist or plastic surgeon for your scar treatment. There is a full panoply of treatments available that do work: surgery, laser, peels, dermabrasion, fillers etc.