Dear Varun,
If you feel that after an year the refund claim is untenable then you can very well write to the previous employer stating that you have been issued with a "No Due Certificate". Therefore, after an year the refund claim cannot be entertained.
However, there is a downside of holding on to his position. One is that your ex-company may send a notice to you with CC to your current employer. A tactic of marking copy of the letter to the current employer may used so as to bring mental pressure on you to refund the excess payment. If your ex-employer comes to know about this case, they may start asking unnecessary questions and you may be cast in unflattering light.
Else your ex-company may send you the lawyer's notice and copy of this notice also may be sent to the current employer. However, this possibility will arise if the amount involved is big enough that merits lawyer's notice.
Lastly, be aware gentleman! Life is too uncertain. There are always ups and downs. Who knows you may need help of your ex-company for some or other reason. If you take a tough stand then the doors of taking help will be shut permanently. In contrast, if you pay the amount then the door will be left ajar for a long time.
Therefore, the choice is yours!
Thanks,
Dinesh Divekar