How Can I get Xfinity to honor the Promises Made by Their Customer Service Representatives - Feeling Lied to and Cheated

Switching my cell phone plans to Xfinity has been the absolute worst experience I have had with a provider. The first customer service representative told me the offer, and promised to call me back the next day so I can confirm the order after speaking with my family.  She did not call until a few days later at a time I couldn't speak.  She wanted to be the one I worked with so I asked if we could talk at a later time and asked if I would lose any of the offer amount if we did it at a later date, and she promised I the promotion would not change.  She did not call back so I contacted Xfinity and spoke with another agent.  The promotion the previous agent offered did expire (first lie told)  but the current promotion was acceptable, even though the trade in value was less that originally promised.   I was also promised a significant discount on my internet/cable bill (by both agents) if I switched my phones from my current provider.  I spent a significant amount of time on the phone getting the transfer of multiple phones set up, just to have them cancel the order the next day.  When I called back to get find out what happened to the order I was told that the wrong ID was uploaded (a reason that the first agent failed to clarify) and the phone trade in promotion had ended and I would receive less for the trade in phones if I switched now.  I told them if they were not going to honor the original order I had placed then to cancel everything.  They told me they would honor the order but the difference had to be in a one time bill credit for the difference on each phone and they would still honor the discount on the internet/cable.  I asked them to please place the same order then if they were going to honor the pricing.  They kept me on hold for well over an hour while they reprocessed the phones, which included ported numbers, and at the end told me everything was good once the ID was uploaded.  They could not figure out that they sent the ID upload link to the  land line I was calling from, which waisted another half hour plus of my time with the agent telling me I had to go to the store in person to figure it out.  My husband then had to call separate and spend more timing getting it handled just to place the order.   When the phones were received, they were all assigned new phone numbers, which then required a significant amount of time on the phone trying to get that straightened out in order to have the ported numbers on the new phones.  Then came the billing.  The promised credits did not appear on my bill neither did the discount on the internet/cable bill.  I called and spoke with someone about cable/internet and they could see in the notes that the monthly discount was promised but they couldn't figure out how to get it on the bill and told me to call back closer to the billing date to get it done.  That's unacceptable.  I then had to call separately to get the mobile phone credits added to my bill, which the agent promised me would show up on my bill as they were also able to see that the credit were promised in the notes and there would be no reason for me to call back because it would just take a few days and the credits would show up.  I was billed today and no credit were applied.  I absolutely dread calling back to speak to yet another agent that will lie to me but need to get this resolved as it is a significant amount of money promised, as they acknowledged on the notes and can go back and listed to the recorded calls.  I have dates and times and agent names.  I am looking for an email or a way to connect with a customer service representative in writing that can resolve this issue.  As much as I like the Xfinity products, if this is how they are going to continue to treat us as a customer, I will look elsewhere for a provider that doesn't lie and cheat their customers.