If it is a 4G device, the info updates on it's own. If a 3G device, dial *228 and choose option 1. Many say choose option 2, which you can, but I always felt 1 was a better option.
If you do have a 3G device, what you may be seeing is the tower being updated partially to 4G. To do so a 3G antenna in most cases needs to be removed. And if that antenna happened to be pointing your direction, then yes service would deteriorate.
If you have a 4G device, I would call tech support from your landline and have them file a ticket to check the tower.
800-922-0204, option 3.