This is a known problem. See:
http://money.mvps.org/faq/article/114.aspx
which suggests removing the bill from the budget before deleting it and which also contains this link:
https://support2.microsoft.com/default.aspx?scid=kb;en-us;318841
with some additional (rather unpleasant) options.
Before you do any recovery attempt, be sure to save good backups of you current file in a safe place so that you can recover if something goes awry. Then, if you have a backup from before the date when you deleted the first bill, the simplest process
it to open that backup file, delete the bill from the budget, and then delete it from the bill summary. This will require that you then "catch up" the file by entering any transactions that occurred since that backup. Once that is done, you
can enter your new cell phone bill and put it in the budget. Needless to say, this could be really tedious if you backup is not recent.
Another option is the "Remove All Bills Data", aka "Nuke the Bills" as described in the second link. If you are tempted to do this, be sure to read this posting first:
http://umpmfaq.info/faqdb.php?q=187
Let us know how you make out.
FYI, Microsoft Corporate only provides the web site for this forum. They don't monitor these postings or provide support. The support is solely from fellow users.
Bill Becker