我想請問一下They'll make it up on a call by call是什麼意思？

They'll make it up on a call by call
因缺少前述實在很難了解其意思，網路上查了一下，或許(只是或許)是與手機有關.
They'll make it up(消除) on a call(一個來電) by call(以事先鍵入該號碼阻斷該來電的方式為之)？
網路叁考資料
Can I block my number on a call by call basis from my mobile phone?
From your mobile phone, dial #31# followed by the number you wish to dial. This will block your number from being presented to the recipient on a call by call basis.

他們會在打電話後到訪以作彌補.

１．先說＜make it up＞的意思：
他有可能是：補償，撒謊的意思．

２．再說＜call by call＞的意思：
是一個一個地來算的意思．也就是：來一個算一個的意思．

３．所以　整句　在沒有上下文的狀況下　應該是：
他們將會　來一個算一個　看狀況　撒謊／騙騙／敷衍了事．

４．它例：
Ａ：how will we explain this delay to our customers? 我司要怎麼對客戶解釋這次的延遲啊？
Ｂ：Well, let's make it up on a call by call basis. 我們只好隨機敷衍一下吧！