How to treat cobra neck due to over aggressive liposuction 10yrs ago? Had facelift with no improvement (photos)

I am sorry that you have experienced difficulties with the contour of the neck following liposuction.

The images that you have shared show a couple of problems:

- Volume reduction between the digastric muscles

- Volume reduction under the skin with visibility of the bands

For the first problem, suturing of the digastric muscles together will produce a smoother contour (fills the hollow) but will require an open approach under the chin. It can be combined with a slight volume reduction of the digastric muscles is from the lateral view there is still some fullness which I suspect shows more when the neck is flexed.

In general, fat transfer is manageable but may require more than one treatment.

A neck lift procedure can produce improvement for these concerns by adding lateral tensioning to the skin. It may still require a small amount of fat transfer to restore the subcutaneous layer of fatty tissue

Sorry about your neck result. This often happens after liposuction where the platysma muscle bands show through the skin. If you clench your jaw to show your lower teeth, this activates the platysma muscle and makes the middle two edges of the muscle bands stick out through the skin.
Using botox can reduce the activity of the platysma muscle, but if you already see the bands when you are fully at rest (like in the photo), Botox will unlikely help to flatten out the bands.
The indentation in the center of the neck would provide for a nice sharp neck to chin (cervicomental) angle, if the two muscle bands were not sticking out lower than the center area.
During a consultation, I will use an analogy of wearing a dress shirt or sports coat and if the shirt or coat is unbuttoned, when I bend forward 90 degrees, the 2 edges of the shirt or coat hang straight down to the ground with the space between the shirt/coat edges appears to be indented.
If you button the shirt/coat, and lean forward, there won't be an indentation or at least significantly minimized between the two muscle bands because it is a continuous layer of platysma muscle from one side of the jaw to the other.
Not knowing how old you are or having the opportunity to examine you, I am not sure if you need additional skin removal to get the best results. In general, redraping the skin, meaning lifting up the skin then laying it back down and removing any excess skin on the sides gives the best results.
For younger patients under 35, their skin elasticity is naturally very good and the skin tends to contract without need for skin removal. Look at examples of liposuction where the skin appears to contract down without any loose skin. While for others who may have lost a significant amount of weight, they end up with loose skin which will unlikely contract down any further and will need some kind of skin removal surgery.
Hope that helps.
Dr. Yang