What is the ruling on subscribing to "unlimited" electricity and internet services for a fixed fee regardless of consumption?

There is no Shar'i impediment to estimating the rent by duration, because minor gharar (uncertainty) is excusable and hardly any contract is free from it. It does not prevent the validity of the contract. Indeed, Muslims have unanimously agreed on the permissibility of ijarah (leasing/renting) with minor, unintentional gharar.