No Cold Water Supply To Bath Tap!

[3magnet]

We recently had our house rewired...and as luck would have it, the electrician drilled a hole into the hotwater pipe. Luckily they managed to turn-off all the stopcock levers (under kitchen sink & downpipes from both water-butt). Once fixed, they opened all the stopcock valves...all was fine. We had a shower that same night, using both taps, thinking that bothe taps were feeding into the shower head.
Later we realised that the boiler system was off due the the rewiring, and that we used that remainder of the luke-warm water instead of both the cold & hot water supply. We thought nothing of it, until we took a bath the next day. I opened the hot water tap for a while, then the cold water, but the water did not become any cooler.

I then closed off the hot water tap; It is then when we realised that the cold water tap does not deliver any water, but that all other cold water taps in the house do deliver cold water? We then checked all stopcock valves again, they were all open, but they were all realy tough to open and close. We did find that the stopcock valve from the cold water feed coming from the water butt, was seized & did not want to turn either way. It only turned when forced, but it also turned a fastening nut behind it, which should not be turning when you turn the valve.

Any suggestions as to what could be the problem here :?: