Hi,
US numbers have a 10 digit format (after the starting 1). You included 11, but this is likely a typing error. Anyway, check to see that you dial this format: +1 ??? ??? ???? (first 3 digits is the area code). If it doesn’t work there are 2 possible reasons:
1) Your wireless plan does not allow international texting
2) An incompatibility between the 2 networks. An error with texting between the two networks (usually happens when the US network does not use GSM technology).
In any case try contacting your wireless provider to inquire about this.