Firstly please bear in mind that ATC is not necessarily always aware that a pilot is a solo PPL student. If they are, I would hope and expect their instructions to take account of a pilot's relative inexperience. Without a landing clearance, in the circumstances you descibe, you were quite correct to go around.
Many years ago, I was taught to go around no lower than 250' (QFE), if no landing clearance received. I don't know how universal, or otherwise, this teaching may be.
Have you had a chance to discuss this with your instructor? He, in turn, might be able to speak to the ATC unit concerned, to seek clarification.
Last edited by spekesoftly; 29th September 2002 at 12:44.