I bought a matrix sim while going to Mauritius in May 2012. The security amount they had asked for INR 6000 of which my bill was only INR 500. the official had ensured that within 25 days fo return of sim will the money be returned. It is now almost 2 months, that no security has been refunded. Have talked to many of their employees, everyone assuring someone will call me and look into the matter but no one has, till date.
The billing is also highly faulty. I had talked for only 45 -50 seconds per call, but the bill shows that call has been made for 1 mn 1 sec hence charging for 2 calls instead of 1.
Would not recommend using matrix services to anyone going abroad.