Bhai, first of all, just call cc and politely request them to reverse... don't forget to mentioned that you actually paid almost 100% of 2 lac bill timely, but due to some calculation mistake, you missed only 700rs. And it isn't fair to charge this much heavy penalty for missing only 700rs out of 2 lac.
Its quite good probability that they'll consider and reverse the interest amount. Late fee has anyway not been charged since you paid more than min due by due date.
But do remember that it doesn't matter if you miss 700 or 7k, all txns of whole statement are charged interest if full amount is not paid by due date. Understand it like this, assume your billing cycle is 1st to 30th of a month and u did 4 txns in Aug cycle:
1. 50000 on 1st Aug,
2. 50100 on 5th,
3. 50200 on 15th, and
4. 50300 on 20th.
Statement of 200600 generated on 30th Aug, and due date 20th Sep & min due is 10030.
Now you paid 2 lac on 18th Sep and missed 600, which you paid on 2nd Oct (deliberately keeping this date to count 11 days late payment like same in your case). In this case, you paid more than min due by due date, so no late fee will be levied, but u did not pay full due (600 short), so finance charges (interest) will be levied on ALL txns of the billing cycle, till the payment is cleared for each txn. So here is for how much days each txn will get charged:
1. 50000 -> for 48 days (count from date of txn i.e. Aug 1 to date of payment for this txn i.e. Sep 17)
2. 50100 -> 44 days (Aug 5 to Sep 17)
3. 50200 -> 34 days (Aug 15 to Sep 17)
4. 49700 (50300 - 600 (amount that was left)) -> 29 days (Aug 20 to Sep 17)
5. 600 (remaining unpaid amount) -> 43 days (Aug 20 to Oct 2)
Take interest rate as 3.6% per month, lets assume 48 days = 1.55 month and so on, then interest for each txn will be:
1. 50000 -> 2790 (50000x(3.6/100)x48/31)
2. 50100 -> 2560
3. 50200 -> 1982
4. 49700 -> 1675
5. 600 -> 25
And guess what, this calculation is also actually a bit incorrect, because actual interest will be slightly higher.
Reason: I counted 48 days as 1.55 month directly, but that is simple interest. I did that only for sake of simplicity. In reality, banks charge you compound interest, so the sum will be a little bit higher.
Now if short payment was 700 instead of 600, it'd have hardly made any difference as that'd have affected only last 2 components of calculation. Now even if 25k was missed, still only last 2 components would have changed and total would have been 9432 instead of 9032. So remember, when you miss some part of payment, it won't be the part missed that'll cause you pain, but uske corresponding txn ke pehle ke kiye hue paap rulaayenge.