Stop taking supplements for two weeks, then take 1000IU per 10 kg of body weight ie if you weigh 70kg take 7000IU/day.
And don't stress about it, your level is not dangerous. Look on the bright side - you are not at risk of a relapse because your vitamin D level is low
Get tested again, if you wish to avoid conflict with your doctor, try this:http://www.vitamindtest.org.uk/
By the way, my level was just under 400nmol/L and my GP was not at all worried.