You should use the contract class provided by the SDK ( CallLog.Calls in your situation ) when building your queries.
The contract classes are meant to map the object model to the corresponding data names in the database. When the android team need to update a column name in the database, they also update the contract class and then no change is required for developpers.
Then try to change you query string to :
String queryString = CallLog.Calls.NUMBER + "='" + strNumber + "'";
NOTE: the single-quote marks are necessary.
Also make sure the number is exactly matching the database number.
( +33678541236 != 0678541236 )
To be sure to delete the correct row you can do the following :
Cursor cursor = getContentResolver().query(CallLog.Calls.CONTENT_URI, null, CallLog.Calls.NUMBER + " = ? ", strNumber , "");
int idOfRowToDelete = cursor.getInt(cursor.getColumnIndex(CallLog.Calls._ID));
getContentResolver().delete(Uri.withAppendedPath(CallLog.Calls.CONTENT_URI, String.valueOf(idOfRowToDelete)), "", null);
(didn't try it but should work with small corrections)