Comcast unable to honor my new plan that they have previously confirmed

My current 2 year contract was expiring so I went to my account on comcast.net  on Feb 12 and found that there was an option button to "Change Plan" specifically for my account.  I used this and completed the form to acquire a new plan.  I received an email confirmation.  Four days hence, on Feb 18, I was not getting the internet speed for the new plan so I entered chat to rectify this.  I was told that I did not have a new plan.  I pointed out that when I look at my account info under the heading "Legal Agreements and Contracts" my prior approval was documented in detail.  Despite this, after about two hours of chat I gave up and agreed to a more costly payment for the same plan that I had previously been approved for.   Today I can still go to my account and find that my original plan remains on offer.   Anyone else experience a similar problem with renewing your contract online please let me know.