In store rep changed my plan even after i confirmed no changes. Whats my next step?

So on black friday i got a pixel 9a for $6 a month with a $50 plan.

I went in store today to exchange the 9a for the 9. I confirmed that the plan wouldn't change ... sales rep agreed. I asked if the $50 plan was still my cheapest option and she said yes.

She told me it was a straight exchange and no plan changes. I didnt sign anything.

I get home and seet my plan is now $70.

Race back to the store and she is saying it is a system glitch and shouldn't have happened.

She called their service number and the phone rep said to change my plan i have to pay out a $1200 tab balance for a phone ive owned for an hour.

The in store rep has now sent an email to her higher ups seeing if they can make an exception.

This is crazy! I confirmed my plan wouldn't change before agreeing to the transaction. Im not paying for her mistake... if the escalating does nothing, what are my options? Return the phone and go elsewhere? Anyone I can escalate to myself instead of the rep that messed up escalating on my behalf?