I need help getting root access on my Galaxy S4 (SM-S975L)

I recently bought a Samsung Galaxy S4 SM-S975L from Walmart and used towelroot. It worked but only temporally. Then my phone messed up and I took it back to Walmart to replace it. I got the same exact phone again but towelroot says that it doesn't currently support my device. I've tried everything out there and was just wondering if anyone could/would help. Thanks