I also recontracted on the 5th and appear to have lost the boost - had gone from 50 to over 60mb, and now back to just about 50mb.
I have made 3 or so calls, as well, and am getting nowhere!
Depending on the type of fibre broadband you have installed, you may have posted this is in the wrong forum (as I did earlier!)
If you have FTTP (Fibre To The Premises), then you're in the right thread. But if, like me, you have FTTC (Fibre To The Cabinet) you're not.
However, I'd suggest you check which you have and then start your own thread in this forum so the mods can give you personal support.