Add event on S3 using CloudFormation - 'bucket already exists' error - amazon-web-services

Question

I am trying to create a lambda function with a S3 trigger. While executing the templates, I am getting S3 bucket already exist error. There is no any buckets with the same name in my S3 and even in this code I am creating bucket only once but somehow it seems it is creating buckets twice.
Below are the my cloudformation templates.
'''python
AWSTemplateFormatVersion : 2010-09-09
Parameters:
BucketName:
Type: String
Resources:
Bucket:
Type: AWS::S3::Bucket
DependsOn:
- ProcessingLambdaPermission
Properties:
BucketName: !Ref BucketName
NotificationConfiguration:
LambdaConfigurations:
- Event: s3:PutObject:*
Function: !GetAtt ProcessingLambdaFunction.Arn
Filter:
S3Key:
Rules:
- Name: suffix
Value: .txt
ProcessingLambdaPermission:
Type: AWS::Lambda::Permission
Properties:
Action: 'lambda:InvokeFunction'
FunctionName: !Ref ProcessingLambdaFunction
Principal: s3.amazonaws.com
SourceArn: 'arn:aws:s3:::hope'
SourceAccount: !Ref AWS::AccountId
ProcessingLambdaExecutionRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Version: '2012-10-17'
Statement:
- Effect: Allow
Principal:
Service:
- lambda.amazonaws.com
Action:
- sts:AssumeRole
Policies:
- PolicyName: allowLogging
PolicyDocument:
Version: '2012-10-17'
Statement:
- Effect: Allow
Action:
- logs:*
Resource: arn:aws:logs:*:*:*
- PolicyName: getAndDeleteObjects
PolicyDocument:
Version: '2012-10-17'
Statement:
- Effect: Allow
Action:
- s3:GetObject
- s3:DeleteObject
Resource: !Sub 'arn:aws:s3:::${BucketName}/*'
ProcessingLambdaFunction:
Type: AWS::Lambda::Function
Properties:
Code:
ZipFile: !Sub |
import json
import boto3
s3 = boto3.client("s3")
def lambda_handler(event,context):
print("hello")
Handler: index.handler
Role: !GetAtt ProcessingLambdaExecutionRole.Arn
Runtime: python2.7
MemorySize: 512
Timeout: 120
'''