SVC occlusion

My SVC is completely occluded (by a thrombus). Both of my jugulars and several other veins are also occluded. I've gone through 2 surgeries in an attempt to reopen my svc and place a stent, neither of which have succeeded (could not penetrate the thrombus). My collaterals are currently handling the venous load, but it comes with some pretty significant symptoms. I need suggestions as to where to look next to find a way to get this fixed.