1.Iamwritingtoexpressmyconcern/gratitude/apologiesregarding…
2.Thankyouverymuchforyourkindassistance.
3.Iwouldliketobringtoyourattentiontheissueof…
4.Ihopeyoucanunderstandmysituation/concerns.
5.Pleaseletmeknowifyourequireanyfurtherinformationorassistance.
6.Iamlookingforwardtohearingfromyousoon.
7.Yourssincerely,(formal)/Bestregards,(informal)
8.Pleasedonothesitatetocontactmeifyouhaveanyfurtherquestionsorconcerns.