Sorry everyone has ignored you.

If the plant is still alive, I suggest you gently probe at the stem to see if it is rotting. If not, it may have a root problem.

You didn't mention how low the temps went before you brought it in. If below 50, it was already failing.

Then, too, you must have a very bright place to keep it indoors. Even then, leaves will drop because they grew while in full sunlight. They must be replaced by shade-grown leaves while the plant is indoors.
It appears to be in tough condition and may not survive. It is very weak and spindly. Perhaps it wasn't in top condition when it came indoors thus, was unable to make the required adjustment to survive.

Consider replacing it when fresh plants are available in spring.

Jean,

Appreciate the feedback, when the plant was bought indoors it was still with flowers at an outdoor temp of 55. Its leaves fell and these were the new indoor or shady leaves which are now falling. I cutback with water till the soil was dry and then watered but it didnt seem to help, its in the basement so gets light from the home lights.

Bougainvillea really likes strong sunlight and hot weather. If you have to bring it in over the winter, give it the brightest possible light - a south-facing sun porch - and minimal water.

Where do you live?