It is possible that you are on the seller's Blocked Buyer List. Usually this is because you have Unpaid Item Strikes.
Have you tries using Messages to contact the seller and make your offer?
In addition to the phone lines, manned by subcontracted minimum wage workers with little training and no authority, you can use Chat, eBayFaceBook or eBay Twitter.
These are written not oral reps, but they actually work for eBay.
https://twitter.com/askebay
https://www.facebook.com/eBay/
Seriously, you will get more useful help with you keyboard than with your voice.
Just redirected to an off site chat help line that charges one dollar but needs all your CC information.
SCAM!!
EBay does not charge for Help.