A <- read.table("123.txt", sep=",",col.names=c("date", "data"))
A$date <- as.POSIXct(A$date, origin="1970-01-01", tz="GMT")

plot(data ~ date, data=A, type="l", lty=1,col=2,xlab="Datum",ylab="Verbrauch", xaxt="n")
axis.POSIXct(side=1, x=A$date, at=A$date, format="%d.%m.%Y")