I’ve had Mint. No problems at all. Easy to setup and good telephone customer service. I left them because the only way to get the cheap rate was to pay either 6 months or 12 months in advance (I forget which).
I went to T-Mobile which is $16.50 drafted monthly for unlimited talk and text and 5 gigs of data (which, with wi-fi access, I’ve never come close to using that much).
So, no problems with Mint’s service but I’m very happy with the the T-Mobile plan and service. It is considered to be a pre-paid account but since it is auto billed/drafted monthly it is no hassle. Good luck!