Your system is fine in theory but hopeless in practice. As a landlord I am responsible for the bill between tenancies even if there is no energy used and the gap is very short. Usually suppliers simply waive the bill, or just charge standing charge which should be a small figure for 4 days. I have had to join and since then have absolutely no idea what is happening, nothing has come from Pure Planet except radio silence. No ability to call, to email, to do anything, so will have to give up.