Agent said I could replace my new phone with cracked screen, then charged me $500!!

I recently signed up for your Xfinity mobile service after being with my provider for several years.  I have had a lot of issues trying to get help when I talk to an agent, everybody seemed confused and I kept having to tell them my story over and over again. I took advantage of one of your offers, the deal said if I transferred my phone number, I could get a new phone, and the monthly charge would be waived as long as I stayed with Xfinity mobile for a year. I went for this deal but within a few days, my new Android phone had a cracked screen. As an iPhone user, I have never dealt with this problem before. After hours on the phone with one of your agents, he reassured me that  I was still within the timeline to send this phone back and get a replacement. Since I had purchased the deal less than 14 days prior,  I sent the phone back. I also ran into problems with transferring my phone number, and I wated for two weeks, after contacting Xfinity Mobile several times to ask that they port my number. Having to wait over 2 weeks to be able to use my phone again impacted my work at home since I work remotely. Days after receiving the replacement phone, the phone with the cracked screen was returned to me within a few days, badly packaged and with an even bigger cracked screen!!. I received an email saying that I owed Xfinity $500 for the phone after the agent on the phone reassured me days before that my phone was eligible for a replacement!!!. Even worst! my first monthly bill reflected a charge for the replacement phone that was sent to me as well!
The deal I signed up for with the Xfinity mobile said I would not have to pay a monthly charge for any phone, but now I owe $500 for a phone with a badly cracked screen that I only got based on an online offer, I have another phone that I am being charged for monthly, and my phone line was disconnected after talking to one of your agents again for 2 hours and telling them my story. After all that time on the phone, I was told I would have to pay the $ 500 to have my line restored. I even offered the agent to keep that phone with the cracked screen!! He didn't know how to have my phone service restored.
I have been trying to pay my monthly bill for 4 days. neither the website nor the app will allow me to make any payments.  the moment I contact Xfinity mobile, this large balance  I am trying to dispute triggers the system to end my call if I don't pay.
 I would like someone to help me solve the situation.  I am currently dealing with a family emergency. I haven't had a service for several days, and I work remotely. I understand that agents are very new to Xfinity mobile policies and services. But I signed up for a deal, and I agreed to a contract that specifies I would receive a new phone free of charge as long as I  kept my service. Instead, I now have two phones for which I am paying or expected to pay, no phone service, and your agents seem to be unable to help me. I appreciate it if someone contacts me to resolve this emergency. All I wanted was freedom from my previous provider and a good phone deal to go with it!