Need to cancel service after moving out, unable to call from overseas

I moved out of my service address at the end of May and forgot to cancel my internet service. I have been billed for several months since then even though nobody has used the connection.

I have tried the Xfinity Assistant chat, but it keeps telling me to call in. I am currently overseas and cannot reliably make a US phone call, so I need to handle this over text.

Could someone from the support team help me:
1. Cancel the account, with the disconnect backdated to my actual move-out date
2. Review a refund for the charges billed after that date
3. Send written confirmation to my email

Happy to share my account details privately. Thanks.