Try rebooting your modem. That got it for me (the increase, not the notice of an increase).
I actually just changed my modem today because I was using Comcast's modem/router combo and wanted to use my own... I'm still at about 50-60mbps. I guess I will contact them again.
I talked to them and they say I am still on the 50/20 plan... they replied saying I would need to pay more to get 100mpbs. I don't need it, so I won't.
Xfinity bumped the lower tier plans earlier in the week or maybe last week. They obviously knew this was coming.