Cellular data for iPhone Mail?

I turned off the cellular data for the Mail only, since that s what uses my data most. Now when I tap to turn it back on, it won't. I tried restarting my phone, tried turning off and on my cellular data completely, still not working. Any other tips?

Couple things to try 1. Try turning airplane mode on then back off. That don't work try removing sim card then replace bk in phone. Hope one these helps