Thermal building blocks, the strange way they build, it is not unusual to see them using thermal blocks but not really built to the standard of insulating.
First the mandatory steel and concrete shell and platform, then the thermal blocks are laid between the shell apertures, no cavity walls and no insulation. the blocks are then usually render over with cement to a rough or smooth finish, then painted. Yes the property has thermal blocks, but absolutely useless with out a cavity wall or insulation between.
There was one company that had started to use cavity walls and infilled with insulation, this was ack in 2004/5 they had to stop this process as it was far to expensive.
Your property probably has got thermal blocks, the contract is not lying, you have not a case for them to answer. You WILL be cold.