As MrSaffron notes, something has changed the parameters of your line, and you have almost no leverage over BT Openreach to get things back to how they were. How much do you value your time and money persevering with ADSL? One engineer visit charge will likely pay for most of the additional FTTC cost for a minimum contract period.
Up to 14Mbps, but I really don't want to go down the fibre route
In your position, I'd go down the FTTC route. You're likely to notice a vast difference between 14Mbit/s and <3Mbit/s, even though 14Mbit/s is relatively slow for FTTC.
I wouldn't worry unduly about the contract length. PlusNet allow you to buy yourself out of remaining months relatively cheaply.