I learnt from this answer that 担当さん is a common Japanese expression to address someone working with/for you. Does the presence of
氏 add a more specific meaning? The context is a letter from a mangaka to her fans:
Considering they are having a party alone and that she later says she received a heart-shaped cake as a present, it could be his boyfriend, but I don't think that's the meaning of My担当氏. Since the letter was handwritten, here's the original to check if I read the characters right. Thank you for your help!