You could post a photo, or you could take the photo to your local bicycle shop and describe your problem to a mechanic.

If you never plan on lowering it , there's always the drill a hole through the post and insert a bolt solution.

THanks eric and rjoh.
I hadn't thought of a regular bike shop!
I had thought about the drilling a hole and putting a metal dowel or bolt through it. It came to me in a dream last night. hahaha

Thanks for your suggestions!

I thought of the simplest fix. A hose clamp. masde of stainless steel. tighten it around the seat post. use 2, one on top of the other to keep it from slipping. Available at any hardware store or home supply store. Couple of bucks for a package.

Here is a link that might be useful: hose clamp

Hose clamps will still slip, I have tried them in applications like this and they don't work well

rough up the surface or use a piece of rubber hose under the clamp. lots of friction there.

rjoh,
So I would put 2 clamps on the post that holds the seat (and goes into the larger tube on the bottom)? I'm thinking even a wide rubber band might work under the clamps, to give more traction??

Yes put the clamps on the post thast holds the seat. Offset the tighteners. Roughen up the post first create some friction. put the rubberbands under them.

The clamps are cheap. any material that does not slip easily under the clamps should work.

Have not done anything like this sionce I was a kid.

Had to fix things best we could.

Thaks rjoh.
Its funny when you said "since I was a kid", I remembered how we would attach cards to our spokes with clothes pin. That really sounded cool! (But maybe you're too young to remember that.)

Catherine: I used to have a bike repair business. If the hose clamps don't work, you might try cutting a strip of metal from an aluminum can, loosening the clamp, slip the metal around the seat post, under the existing clamp, and tighten. OR, take your photo to a good bike shop and talk to a mechanic. They should have at least one solution. Good luck, Steve

Oh I remember that! I am not that young...... born in 57

Thanks Steve.
rjoh.....ah yes, the good old days! :)