@kaia I don't think it's even possible for ISPs to reliably measure 100kB of data usage, as the way transmission works is symbols/time and not kB/time - although the sender/receiver can determine how many MiB of data it sent/received in X time despite the overhead of the transmission medium and TCP or UDP, so a lot of that "data use" is probably made up.

To be honest, an ISP is scamming you if you aren't paying a flat rate per month for a connection of X uplink/downlink (that's symmetrical unless there's protocol/transmission medium limitations on uplink).