my router keeps rebooting what can I do

I'm having the exact same issue. Started about 5 weeks ago. Have been working with tech support without success. On my second modem with a third in the mail. They've replaced the power cable as well. None of this has fixed the issue. 

I hope they are able to resolve this problem for me and you. It is incredibly frustrating although I've been understanding with T-Mobile on the phone. T-Mobile has essentially trapped me financially into their cell+internet plan. I'm technically free to leave, but would suffer significant financial repercussions for doing so. Either increase monthly bills by keeping T-Mobile cell phones and going back to cable Internet. Or, be forced to pay off my "free" phones and go back to Verizon + cable internet.

It's quite unfortunate but I hope T-Mobile can make it right.