iPhone 7 not waterproof after battery replacement

Hey there,

I took my iPhone 7 to an Apple Store to replace the weak battery.

I used to clean my iPhone 7 for about 2 years under water (not longer than 30sec maybe every 4 weeks).
There has never been a problem with water entering the phone.

After the replacement I cleaned my phone again and it got full of water after just 1 second.

I reported this to the Apple Store the next day and the employee told me in a very unfriendly way that there is no warranty and Apple has nothing to do with it.

In my opinion Apple damaged the phone's sealing while changing the battery.

Why should it have always been waterproof and suddenly not after battery replacement?

Apple has to give me the phone in the same conditions back as I gave it to them.

I am convinced, that they did the damage.

What can I do?