incorrect no recharged

On the 18th of March I recharged an incorrect cell no,I realised this during the day and called their call centre who advised there is nothing they can do about this I should call the no myself and request the person to reverse the airtime, I did that but the phone is always on voice mail and called the call centre again and was told the same I feel this is unfair that they cannot assist me in this matter as the person received airtime they did not buy what if this no is no longer in use, I made a mistake must I just loose my money like that,why can they not reverse that airtime 4 me