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Try changing network manually in the phone's connection settings.
Live Chat can check your account settings and roaming terms.
Also if you can try your sim card in another phone just to ensure its not a setting in your current phone that's causing conflict.
Some phone's have some roaming settings in them.
If all else fails you may need to use a local sim card if your phone will acceot one.
It might also be worth checking if the network your latched to is having uts own issues.
Unfortunately Vodafone UK can't always guarantee everything will work as they have no access or control over the local networks in another country.
Current Phone >
Samsung Galaxy s²² Ultra 256gb.
Secondary Phone >
Samsung Z Fold³ 256gb.
The first thing to ask is if you are pay monthly or PAYG. Assuming you are pay monthly my advise here is for pay monthly. If you are PAYG you should only need sufficient credit for making and receiving calls, texts and data usage.
You don't mention the Android phone you are using, not all Android phones support the frequencies for calling from the USA, you will need a quad band phone with wider roaming capabilities. I would suggest checking for any roaming bars on your phone and account, if the phone you are using is listed, you can find further support here: Device Guides
Please see this link for the plan you need to be on to have inclusive roaming Charge Checker Roaming .
You should have received a text message when arriving in the US welcoming you to the country advising you have connected to an overseas network with details of charges. If you are going to be charged £6.00 per day, Vodafone apply a credit limit to the account and you would be unable to make calls once the limit had been reached.
If you have internet, it might be worth dropping the Social Team a message through Twitter or Facebook, they will be able to check your account here: Contact Us