Unable to call my other polcom line

I have been using airtel polcom with my wife for three months. But, just yesterday after our subscription of N700 each, I was not able to communicate with her because my account is too low...I checked my polcom account and the minutes were given as expected...And, I checked my tariff plan which is still polcom but I can't use it...But my wife can use her line to call me....Please, help me....Thank you!