Lambda, updating Cognito custom user attributes doesn't do anything - node.js

Question

iv been setting up a lambda instance, it grabs data from a few different services and then its meant to update a custom Cognito attribute for that user, that works correctly and i get the return response "{}" along and no errors so im assuming that means its working correctly, however when i check the users attributes its not returning anything?
i have triple checked that the app clients have read and write permissions, so i have no idea whats happening, everything, as far as i can tell, is working, just that the attribute isnt changing.
return new Promise((resolve, reject) => {
console.log("TestInside");
// setTimeout(function() {
console.log("TimeoutFunction");
var cognitoidentityserviceprovider = new AWS.CognitoIdentityServiceProvider();
var params = {
UserAttributes: [
{
Name: 'locale',
Value: UserFarms
},
],
UserPoolId: 'UserPoolID',
Username: UserName
};
console.log("Executing call");
const cognitoD = cognitoidentityserviceprovider.adminUpdateUserAttributes(params, function(err, data) {
if (err) {
console.log(err, err.stack); // an error occurred
//passon = err.message;
resolve('Error');
}
else {
// cognitodata = data;
console.log('Returned positive cognito admin update');
//UserName = data.Username;
//passon = data;
console.log(data);
resolve(data);
}
}).promise();
whats wrong, am i missing somthing really simple?