Am I correct that this is really the ONE bank account and you created a second QBs account?  If so, do both QB Accts show the Bank Acct# and Routing number when you go into Edit the account.  It's quite possible that Bank Feed is getting confused by the same number being in both places. 

Depending upon how much work you've done in QBs I'd suggest two things, just to get back to "normal" and then figure out where to go next:

• FIRST, MAKE A BACKUP
• Option 1: If you've done very little work in QBs since this issue came up, Restore the backup from when you added the new Acct and then just re-enter whatever you had entered over the last couple of days.  (Make notes or print reports before you start this if you need extra info like check numbers, amounts, etc.)
• Option 2: If you've made multiple changes in various areas of QBs it might be easier to just make all the changes and then delete the new QBs Bank Acct.  (I like Opt. 1 because it's clearner.)
  • Go through the new 2020 register and go back to each transaction and move it to the old register.  This will probably include going to a Bill, deleting the payment and then making a payment using the original account. 
  • Do all of this slowly and carefully (but pending where you are in the country, regretfully you probably have time on your hands).

Once you have everything back to where it was, then make sure all the Bank Feeds are disconnected and possibly even run QB's File Doctor to make sure there are no issues still pending.

So above are my (not so pretty) thoughts on how to get back to square one.  But now I have to ask why??....

Again, assuming one bank account, I'm curious why you would want/need to create a new QBs Acct/Register for 2020?  I have an active checking account in QBs going back to the 1990s.  And I think my Accountant might not be pleased if I suddenly made it look like a new bank account.  I'm also going to assume that you had 2019 checks that didn't clear until the January 2020 statement.  And at the end of this year, you'll probably again have 2020 checks that will not clear until 2021.  So you really can't create it by year. 

Within QBs you can run Checking Acct Report just for 2020 as well as a number of other reports by year.  That includes your Profit & Loss statement which is really one of the go-to reports.  So even though I'm someone that likes to make payments early in Dec. so they checks will hopefully clear and even pay the current balance on my credit card on 12/31 to try and have the YE nice and clean, I still would never create a new QB Acct for a pre-existing bank account.

Just my 2 cents.