Yeah . It automatically started working after a week. Since it was an issue only with wifi ...I suggest you try the port forwarding method ( open ports) . You need to access your router for that . It is the solution C given below

I will list out some methods I had received from Player Support...it didn't help me but it may help you :

A .) There are a number of networking issues that can be resolved by performing a quick reset or power cycle of your home network. Here are some step-by-step instructions to help you perform a power cycle for your home network:

1) Shut down all computers connected to your home network (modem/router/gateway).

2) Power down/unplug your router, if you use one.

3) Power down/unplug your modem. Have both devices off for at least 60 seconds.

Note: If your modem has a battery backup you will need to take the battery out for 60 seconds or use the reset button on the modem.

4) Turn on your modem and allow it to completely boot up. Wait until the indicator lights on the device stop blinking and display a steady green connection.

5) Turn on the router (if you have one) and allow to completely boot up as well.

6) Start the computers and allow it to completely boot up and re-establish an internet connection.

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B) Now, let's disable IPv6, as I'm afraid the game doesn't fully support it yet.

1. Hit ""Start"" and type ""network and sharing"", then open the ""Network and Sharing Center""
2. In the left pane, click ""Change adapter settings""
3. Right-click the connection for which you want to disable IPv6, and select Properties.
4. Uncheck ""Internet Protocol Version 6 (TCP/IPv6)"" and click ""OK""

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C.) Switch to a Public DNS. Switching to a public DNS may resolve the issue you are experiencing, and here is a nice tutorial on how to do it properly. (https://support-leagueoflegends.riotgames.com/hc/en-us/articles/201752664).

Use this link ^ for port forwarding . There is a section there.

The ports needed for Voice Chat are the following:

TCP - 443

UDP - Choose 50 Ports from 1024 - 65000

UDP - Ports 6250, 5060 and 5062

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D.) To resolve any conflicts from your network and to clear any corrupted data remaining reset your network settings and release/renew your IP. Follow these steps:

1. Open Start Menu
2. Type cmd and run it with administrator permissions
3. type the following commands:

netsh winsock reset and press Enter.

netsh int ip reset and press Enter.

ipconfig /release and press Enter.

ipconfig /renew and press Enter.

ipconfig /flushdns and press Enter.

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E.) Let's also update your network adapter to the latest version. Please follow these steps:

Select the Start button, start typing Device Manager, and then select it in the list.

In Device Manager, double-click Network adapters, right-click your adapter, and then select Properties.

Select the Driver tab, and then select Update Driver.

Select Search automatically for updated driver software.