alan_m explained :
Most companies do not contact you to offer a new deal or even to say that
your old deal is coming to an end. They make more money by just placing you
on their standard variable tariff and hope you don't notice.

I think they are legally obliged to let you know when your contract is
coming to an end. Certainly every company I have been with recently,
has emailed me to let me know and advised what tariff I would be moved
to at the end. Even if they didn't, I'm signed up with MSE to let me
know and make suggestions as to which supplier and tariff would be my
best one to move to.

I get the same notices for car and house insurance, changes in interest
of banks and investments, pensions etc..