Before I signed up to BT FTTP I was told that specifically on the 900Mbit plan, I could get a static IP. I made a note of asking the guy TWICE to make sure he understood and he did, and clearly stated I just had to call to get one.
Salespeople get paid commission for making a sale, not for telling the truth. Whether or not he really knew what a "static IP" is, he gave you the answer you wanted to hear.
Unless you have a recording of the phonecall, then there's little you can do. Even then, the best you could hope for would be an early release from the contract.
As others have said: an FTTP connection with a stable router will keep the same IP address for weeks at a time, and dynamic DNS can take care of the rest.
If you want a real static IPv4+IPv6, then you can pay £10 per month for the AAISP L2TP service, and access it over your BT FTTP. The L2TP tunnel is limited to 100Mbps up and down, and 1TB per month, but you could use it for incoming access, while outbound connections still go over the native WAN link. (You need a router which is sophisticated enough to handle this sort of routing policy though)