Hi Sandeep,
Did you check the ICM trace in your on-premise CRM system to see if the call reached CRM in first place? If it did not reach CRM system then it get stuck somewhere in the middle like reverse proxy or firewall which is sending back a HTML content type as the response.
Also did you refer to the Connectivity FAQ http://scn.sap.com/community/cloud-for-customer/blog/2014/10/29/connectivity-faq--integrating-cloud-for-customer-with-sap-erpcrm
as it stated that if you are using anything other than port 443 then create a ticket to check on what ports can be used as it may vary from region.
Thanks,
Prakash