Phone call showing in two months

[#1]

Got a strange one...made a chargeable phone call on the last day of my charging period (4/2) ....it has been charged for in the total month's invoice, but appears in next month's itemised bill in the Home Phone control panel not in the month just gone.
Raised a ticket 2 days ago -65436527 - no response as of yet- just don't want to pay twice for the same call!!

[#2]

Now had a reply to my ticket to say that I won't be double charged but............ WHY is the call invoiced in the correct month but showing in the calls summary for the wrong month? Sounds like a system error to me.!!