Fillers are not used to treat platysma muscle neck bands. The bands are the result of the contracting of the platysma muscle of your neck, a dynamic process, that cannot be improved with fillers.
You have already had a neck lift, and you may or may not have had treatment of the neck muscle bands as a part of the neck lift procedure. So, it would be helpful to know what was done for the platysma muscle bands.
At this point the best option may be the use of Botox to weaken the platysma muscle contraction which is the cause of the bands.
It is important to keep in mind that there is no perfect surgical procedure for this problem, and that even with initially good results, platysma neck muscle bands may form again.
You should discuss your concerns with your plastic surgeon who is already familiar with you. You may also want to get a second opinion consultation with a board certified plastic surgeon who can evaluated anew and provide a fresh prospective on your concerns.