I don't think there is anyway to get a refund on PS3.
A physical copy would need to be taken up with the retailer who sold it.
A digital copy would need to be taken up with Sony since they control the PSN store.
*edit* Game stores will accept used.. but the price they will offer will be low compared to what you paid.
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What NAT type is your PS3 in connection settings?
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Perhaps try manually forwarding the ports? Set a DHCP Reservation for your PS3's MAC address so it doesn't change.
http://help.ea.com/en/article/online-ports-for-battlefield-4/
(same as BF4)
You could try putting the PS3's IP in DMZ to test.
If you have modem in front of your router you could try directly plugging into the modem to test. This may help narrow down the problem.
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Try redo'ing your connection settings for the PS3. Make everything Auto.
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You may also try 8.8.8.8 / 8.8.4.4 as a manual DNS (google DNS)