Thanks to this forum I have been able to read my serial number and contact Apple who have arranged a free of charge visit to the Genius Bar on Sunday. I will update on what happens.
In the meantime, I had long since given up in making my Smart Keyboard work and bought a replacement from Amazon.
https://www.amazon.co.uk/dp/B078NSNZKY/ref=cm_sw_r_cp_awdb_t1_pc5wDbA8YFSJ9
This cost me £15.99, works a treat and I actually think is better, if not quite as convenient, as the Smart Keyboard. It still fits in to my neoprene iPad case with my iPad and I now only use the Smart Keyboard as a (very expensive!) screen cover.
I agree that Apple have, and continue to, really let themselves down here. When I spoke to the support team they ran through some trouble shooting steps, all of which I had tried, except the final one when they asked if I’d tried it on a different iPad Pro … erm, do they know how much iPad Pro’s cost? I don’t have another iPad Pro!!