configuring network between two sites

Hi Guys,

Hope this post is suitable for this reddit.

in my company we have two departmets that are physically located 5km apart. We just switched to fiber internet and were offer by the provider to deliver to one department direct internet access and to the other something called data transfer. The provider claims that these two can be connect so we get access to the internet in both departmets and do't have to pay for two internet lines.

So in depatment 1 - HQ we received from the provider a switch with 2 active ports. Port 1 is for internet and Port 3 is for LAN. We connected our router to port 1 of the providers switch and our local switch to the router and everything works fine.

In department 2 we also received a switch but with only port 3 active for LAN.

Now here is the troublesome part. The provider claims that we should connect our switch in HQ (department 1) to port 3 on providers switch and then connect a computer to port 3 on the other providers switch in department 2. As a result the computer in department 2 should be able to access the internet. Well it isn't.

The interesting part is that when I connect the computer to port 3 of the switch in depratment 2 the leds on the switch turn green and the computer claims that it cannot identify the network. However on the other end when i connect local switch to port 3 on the providers switch in HQ leds are dead. But when I direcly connect a computer they turn green.

Can anybody help me? What am I doning worng? Should I make some special settings?

The local switch is a cisco SG200-26, the providers switches are SG300-10

Thanks

Visual description-> https://imgur.com/a/1b6eOkk