How can I remove my sloped chin / neckline and have a more defined jawline? (Photo)

Based on your pictures just a simple neck liposuction procedure may be enough to help your chin-neck contour

You need to remove more fat, tighten skin and possibly reposition the platysma muscles. There are several options for doing this and I would need to perform a thorough exam to determine which technique(s) is/are best for you.

 From the pictures presented, it appears there is fatty deposits located both above and below the platysma muscle. Closed liposuction can only partially remove the fatty deposits above the platysma muscle, that's why it was ineffective with the first procedure. The fatty deposits below the platysma muscle must be removed with a surgical neck lift which includes a platysma-plasty. No skin removal is required, since you're only 33 years of age. Three small access incisions are performed underneath the chin and behind the ears.  Open liposuction accomplishes a better and more complete removal of the fatty deposits above the muscle, while surgery removes the fat below the muscle and then the platysma plasty tightens the platysma muscle and significantly improves the jawline. This procedure is performed under general anesthesia as an outpatient procedure. Anticipate two weeks of visible bruising and swelling. For many before-and-after examples, please see the link and the video below

 Hi, I have performed many facial shaping procedures using dermal fillers, silastic facial implants (cheek, chin), liposuction and/or facelifts for over 30 years.  From the photos, your cheeks are very flat in the front, the chin itself however is not weak but there is excess skin (no fat) under the chin.   nose has a dorsal hump with a nasal tip that is under rotated (makes the nose appear long).  These combine to create an elongated, thin, rectangularly-shaped face.  
 Following my beauty principles, women look the most feminine, youthful and attractive with heart shaped faces.  Heart shaped faces have cheeks that are full and round in the front.  Cheek augmentation with a dermal filler or using cheek implants (for a permanent enhancement) will create full, round cheeks that will feminize the entire face.
 The excess skin under the chin can be removed using a small, curved, incision under the chin.  
 The back portion of your jaw line is a bit weak and can be augmented, without making your face appear masculine, using precise placement of a dermal filler (I prefer using Restylane Lyft).  
Hope this helps.