Can you please expand on these questions:
1. Are there other users in your house connected to internet in same time when you have these issues?
2. Have you tried to connect to router with LAN cable, and does that work?
3. Do you recall doing anything on your PC or router prior this problem or is it present since ever?
Here is user manual for your router:
RAC2V1S Sagemcom Wave 2.pdf (d15yx0mnc9teae.cloudfront.net)
If this issue started only recently it's likely not router issue otherwise the manual does not mention NAT settings but if there is one you can find them probably under either "router settings" or "Internet connectivity"
Let me know if there are NAT settings.
To log into router enter this default address into your browser address bar and press enter:
http://192.168.1.1