This is tough. . . Here are a couple approaches:

1) Sit down with your mom at some quiet time (NOT when a
package has just arrived) and try to talk to her about it.
Try the angle of: "This is something I really enjoy. I know
you don't think much of it, but I would like to share my
enthusiasm with you." (Obviously those exact words are
corny, but I think you'll realize that this really is how
you feel. Stick to ONLY "I statements" ("I feel this
way. . .", etc.) and stay away from the word "you". . .
(This is all integral to the psycology of discussion and
ways of turning a discussion in your favor. A local library
might have books on this topic.)

2) You might want to say: "I have done (XYandZ) to earn my
money and if I wish to spend some on cels, then I feel I am
entitled to do so." (This won't work if somehow you get
your money from you mother - even in a round about way.)
But this is a very argumentative approach and you have to
be willing to *calmly* tell her: "I'm sorry, but that's all
I have to say" and leave it at that. Even if she makes you
sit and listen to a rant, you have to say nothing. She
can't blaze forever, especially if she's getting no fuel
from you!!

3) As a last resort, simply stop talking about it with her.
Tell her that you have been made aware that she disapproves
of this habit, and you respect her opinion, but that you
have determined it is not something that is damaging to
you. Tell her you're no longer interested in screaming
matches. (Again, this MUST be done completely calmly and
MUST be done when you have NOT just gotten a package.) Tell
her that because "the two of us" (phrasing is important!)
can't have a calm discussion about the topic, you will not
speak with her about it any longer. Then you need to stick
to your guns. Say nothing about it AT ALL. If she asks how
much something cost or what you got now your answer will
be: "I'm sorry, we're no longer discussing this." And that
is all you say. Let her shout that she has a right to know
and yell that you're being rude, but simply remain completely
calm and when she's done, just leave without saying
anything. (And don't say anything with your body language
either! Don't storm out of the room - just leave as if
you'd come in to get a glass of water and now you're going
back to what you were doing.)

From the sound of it, you have already told her what some
of your cels cost. Bad idea. Unless you're ignoring a
financial responsiblity you have to her, it's none of her
business how much you pay for anything that you are buying
with your own money, cels included. Also, if she doesn't
believe the cels to be "real" there's no way to prove to
her that they are. Maybe she's heard one too many stories
about e-mail scams and now believes everything on the net
is bogus. You could pay a professional to authenticate one
or two of the cels for you so that you can show her the
professional analysis, but this would be expensive and a
local expert (not someone on the net) might be hard or
impossible to find.

If things continue in this vein, I would definitely have
your cels shipped elsewhere. Perhaps you have a friend who
can accept the packages. Someone else suggested renting a
PO box - a very good idea and usually not too expensive!

Many Sharp Smiles,
--Drac