Credit card operations are under the direct control of RBI. Several guidelines have been issued by RBI on the matter of unfair practices by the card issuing companies. A very important circular letter has been addressed by the RBI to all commercial banks in this regard and I am furnishing the link for the same here.
Reserve Bank of India.
Another master circular appears to have been issued by RBI during the beginning of this year. Though I am unable to trace it in the RBI's web site, I have been able to get the full version of this through another source and the same can be viewed here:
http://www.creditcardwatch.org/Master%20Circular.pdf
In a nut shell, you have to keep safely all the proof of your payments and other correspondence till the matter gets resolved. In the meantime, a complaint needs to be filed with the RBI regarding the unfair practices adopted by Stanchart.
You also need to file a police complaint against Stanchart and their collecting agents for causing harassment and intimidation (Remember to take their names and IDs when they call on you next time). Remain firm with a resolve not to be cowed down with the frequent visits of goons.
Incidentally, a group of lawyers in Chennai have formed a Trust under the name of Centre for Social and Economic Justice and they have filed a public interest litigation in the Madras High Court last month to strictly enforce the master circular mentioned above. In this petition, they have included the Finance Ministry, RBI, IBA and all the credit card issuing Banks as the respondents. The details of the same are available at creditcardwatch.org