I guess I should start by saying that IP prefixes are not technically bought. When an IP prefix is allocated to a provider from an RIR like ARIN, there is no transfer of ownership. The IP range is always allocated to the RIR, and the allocation to the provider is only valid so long as the original terms of the allocation are upheld.
As for the routing part of the question, it is hard to give a specific answer without details on the actual prefixes used; however the most likely explanation is that some providers have policies in place which are not accepting the more specific /24 announcements.
I assume that the site in the US is announcing the entire /19 range, so any ISP that does not carry the specific /24 prefix will instead route towards the covering /19.
As for why some of the ISPs are not accepting the specific /24 announcements, this can have a number of reasons, and to be honest you are only going to be able to get a definitive answer from the ISP doing the filtering; however there are a few things you can try to improve your chances of the announcements being accepted.
Some ISPs will build their policies dynamically from information in routing registries. My experience is strongest in the RIPE service region, where routing policy can be registered using RPSL syntax in the RIPE database. ARIN also have a routing registry, but for the ARIN service region it is more common to register policy with the Merit RADb at ra.net. RPKI is still in it's early days and not many people are using RPKI in their policies; however it is an area to consider for the future which may allow for more reliable route distribution.
As you have seen, if the route is not in the table of these other ISPs then you are not going to be able to influence their routing by means of attributes on your announcements (i.e. as path length, communities, etc). You are only going to fix things by getting them to accept your announcement.