Are you having problems because you are using your phone?
Go to a desktop or laptop computer. The public library has them if you cannot find one at home, work, or school.
Look up the Paypal transaction number.
Note if you pay from your bank account, this causes a delay while the e-cheque clears and may be why your seller thinks you have not paid.
Go to the eBay dispute and tell them that you have paid. Add the PP transaction number. Note if this is backed by your bank account.