Hello,
US phone numbers have the following national dialing format: 1 yyy xxx xxxx. yyy is the area code (both landlines and cell numbers use area codes). How you dial a US number depends on whether that particular call is local or long distance. Generally, to dial state to state you need to dial the full national number (see above). When calling within the same state, leaving out the leading 1 should work fine (or calling the 7 digit number without the area code also works for local calls).
Using 44 or 001 makes no sense. One other option that might make sense is using +1 yyy xxx xxxx or 011 1 yyy xxx xxxx. 011 is the international prefix used by the US and Canada to call abroad (just like the UK uses 00). Dialing +1 instead of 011 works with cell phones.
Let me know if you’re still unable to call.