How do I get my deleted contacs back that was deleted from my phone in error?

You should provide plenty of detail about exactly how you did this phone transition. It sounds like you missed at least one essential step, and cannot recover from this error.

Here’s how the process should have worked.

• Each and every person requires her/his own, unique Apple ID. Sharing an Apple ID leads to disastrous outcomes.
• The iPhone SE should have been backed up. That backup would be the basis for setting up your iPhone 12.
• The iPhone SE needed a thorough wipe before setting it up for your husband’s use. What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

presumably you store your contacts in iCloud..

You may be able to recover them

Restore contacts stored in iCloud on iCloud.com - Apple Support

But you should note that you likely did a couple of things wrong in this process..

Before giving your SE to your husband, you should have erased it

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

Then it sounds like you are sharing an Apple ID with your husband, you should not do that.

When sharing an Apple ID and syncing contacts in iCloud, when deleting from one phone, you delete from the other.

Here is what I would do, keeping in mind that I've never done this.

I would attempt to restore your contacts using the first link I provided.

Then I would check to see if the contacts show back up.

Once they do, I would sign yourself out of your husbands iPhone.

(probably not erase it at this point since information is present from his flip phone)

Then sign in with his Apple ID. If he doesn't have one, create one for him.

Sign out of iCloud on your iPhone, iPad, iPod touch, Apple TV, or Mac - Apple Support

How to create a new Apple ID - Apple Support

Then if you want to share content, look into family sharing

Set up Family Sharing on iPhone - Apple Support