TP-Link mifwi won't connect to internet

Hola

I've just put a new T-Mobile sim in my TP-Link M7010 mobile wifi unit and it won't connect to the internet in USA. I can connect my phone to it and it appears to have wifi, but it won't open any websites or download emails. Status says connected but no internet. Any suggestions on what I should try? I had the SIM activated in the T-Mobile shop, but they didn't know what to suggest. I've tried it in 2 different mifi devices; one from UK and the other from Spain. Thanks