While out at Condado last week I read in a local paper about the way Iberdola bill for electricity.
Apparently although we receive a bill every 2 months they actually charge every month. However they only physically read the meter every two months and estimate the other monthly reading.
So, because we are all new customers without any usage history, if it drops that they read your meter after or during a period you have used your appartment then that reading will be used as the estimated usage for the following month and a bill generated based on this. Hence the high bills some people have received.
This should even itself out over a period of time.
The news paper article was saying this was a problem for everyone and urging Ibredola to go back to monthly bills.
Hope this helps.