You can try using an api key with your requests, you might be blocked by our service provider automatically for making too many requests too fast.

If you would like to request a Blockchain API key, then you can do via this form: https://blockchain.info/api/api_create_code. Just let me know when it is submitted, and I will approve it for you.

As far as the double spend goes, I'm sorry that this happened, but blockchain is not liable for user initiated unintentional transactions.