Thunderbird and Yahoo mail not syncing

Hi - I can't seem to delete from my Yahoo Mail via Thunderbird. With Yahoo's new mailbox limits I wanted to clean up my Yahoo mail box and Yahoo obviously does not provide any decent tools to support search and delete. I downloaded Thunderbird and despite several deletion attempts my Yahoo mailbox still shows 160,000 emails whilst my Thunderbird client only 9,000 - so when I delete it is not syncing. Most emails are deleted from Thunderbird however some are now reappearing (in Thunderbird). No deletions from Thunderbird are reachign my Yahoo mail inbox, however I can send emails from Thunderbird and see the sent and received email in Yahoo and I can add folders in Thunderbird and see those folders in Yahoo. I tried several things - immeadiate delete in Thunderbird - moving the emails to a folder in Thunderbird and then deleting from that and then deleting the the folder - I check this article https://support.mozilla.org/en-US/kb/thunderbird-and-yahoo and everything appears correct I've had to pay for extra storage to get the code to make this post. Mike