Here's some tech data for you non-geeks.
https://support.managed.com/kb/a604/dns-propagation-and-why-it-takes-so-long-explained.aspx
Basically, DNS changes can take awhile to propogate out to end users everywhere. This can be for many different reasons. Your ISP may cache some pages or your ISP may not refresh their DNS records very often.
OR, as in some areas...you may have XYZ provider, but XYZ is actually the only game in town. You're paying ABC for service, but ABC is merely subcontracting to XYZ and you may not know it.
There is an internet pop down here in Fayetteville with a fiber junction down near some large power distributiion. Some a-hole every other year or so hangs a target on there right before the start of deer season and takes out internet for half of Fayetteville for 2 or 3 hours. Doesn't matter who your provider is, that particular provider is your border gateway on a certain half of town.