Turn off data roaming immediately!
Most places in the USA have wifi, especially the big chains and use that - and if you want to call anyone in the UK, and they use Skype/WhatsApp - use that.
Do you really need data roaming on at all times? If your phones are set to check for emails, that will use data of course and hence can cost a lot for hardly any use.
Data packages for the USA are extremely high for a lot of companies.
Frankly you should have checked the cost and use of data before you left and is recommended for any travel to anywhere.
The cost of calls isn't cheap either. If your phones are not locked, then buying a local network SIM might be the cheapest option.
@Jimkwatson thanks for taking my call. I'm sorry for the delays in getting the add-ons and credits sorted. This has all been done for you now, please post back if you have any more trouble with this in the future.