A helpful post from hallb15. All other schools taking services from ICT4C should follow the advice from Leeds - but contact the appropriate person/helpdesk identified in the letter you received. Despite any other notices you get from other suppliers, you will not be cut off and, if you want uninterrupted service (which a new provider could not offer), wait until your LA has put together the continuity offer which will run until 31/3/18.
If you are taking other services from ICT4C such as reverse proxy, vpn etc, there should be advice/guidance available when you get back from half-term.