Vodafone what is this "roaming call forward charge"?

Hi, I am from surat,gujarat having post paid vodafone no since 2.5yr....I recently shift to mumbai temporary, I continue my gujarat sim but not using it, I bought new vodafone card from mumbai and using it as std call. But my post paid bill shows " roaming call forward charge " rs 500 and 400 in two consecutive bills... I never activated any call forward service in my whole life.....I tried to get costtomer care but all those duffers always put me on hold or just forward call to another big duffer......its pathetic...can any one help me what I should do now????