Ten years old nightmare to make facetime calls to South America
Usually telco supplied WiFi routers are not of high quality. They tend to be low cost varieties with lots of other features bundled in that are of higher priority to the telco.
The best way to proceed is to disable the WiFi functionality in the supplied router. If possible, also disable the routing and NAT functionality to get a bridged connection only.
Then purchase your own router and WiFi equipment of higher quality. This also allows you to place multiple WiFi acccess point different places in the building. For example you typical want to have an access point on each floor (if it's a 2-floor house for example).
You can buy higher quality equipment from lots of different manufacturers. A popular choice for WiFi access points would be Ubiquity. If you do not have experience with WiFi equipment, I would recommened getting a professional to install said equipment. Around here it is very common to get offers on WiFi equipment including installation - I don't know if the same goes in that specific location in South America.