Sculptra didn’t work - what do I try next? Radiesse?

If Sculptra did not provide the desired results, other dermal fillers may be an option for you. Radiesse is one such product that could be considered. It's a calcium-based filler that stimulates collagen production and provides immediate volume.
However, the choice of filler very much depends on your individual needs, desired outcomes, and your healthcare provider's professional opinion. Other options might include hyaluronic acid-based fillers like Juvederm or Restylane, which are often used for facial wrinkles and folds.
It's important to have a thorough discussion with your healthcare provider or a dermatologist about the best alternatives for you. They can guide you through the options based on your skin type, age, and desired results.
Remember, results can vary greatly from person to person, and sometimes multiple treatment sessions are required to achieve the desired effect. Therefore, patience and realistic expectations are key when undergoing such procedures.

Frontal and profile view photos of your neck would have been extremely helpful for advising you. Aging necks with sagging and jowls can result from a variety of causes, indluding insufficient chin projection, loss of definition of the jawline, platysmal hyperactivity, etc. And, in the hands of a sophisticated, experience injector, the precise nonsurgical treatment or combination of treatments depends upon what cosmetic issues need to be addressed. Shotgun cookbook treatments, such as Sculptra--which I gave up using nearly a decade ago-- or the use of expensive gizmos that have little hard science to support their use (but a whole lot of marketing hype ans social media buzz), such as fraxel lasers, RF devices and ultrasound machines often prove a waste of money, and time. However, appropriately robust HA fillers can help to straighten and define jowly jawlines and secondarily improve submental sagging. They can increase chin projection, if necessary, to further benefit the aforementioned. Botox can soften playsma muscle verical cords in what has been called the "Nefertiti Lift." Robust HA lifting fillers injected appropriately around the neck can diminish sagging and skin boosters and/or Profhilo can help to improve midline skin quality and reduce crepeyness. You would be wise to make sure to consult an experienced, board certified cosmetic dermatologist. Best of luck.