Dependant Visa Issue

I applied for visa extend and i made the payment IHS but system just charge 517.50£ and then i paid visa payment. I know ihs charge is 1024£ why happened this idk but it is not my fault what can i do now?

I applied for visa extend and i made the payment IHS but system just charge 517.50£ and then i paid visa payment. I know ihs charge is 1024£ why happened this idk but it is not my fault what can i do now?