If all the wires are connected in the office jack you have both lines there. Red/green is one line and Yellow/black is the other.

As hendricus says, you should have both at the office jack. Plug a phone in there and see what happens. Sometimes, all 4 connections are in place but only 1 line is active. A telephone with a line 1 and line 2 button would confirm that. You could also disconnect the 4 wires and where the black and yellow wires were, connect the red and green. If you do this and you get dial tone but can't dial out, switch the red and green wire connections.

Did the telco do the inside wiring? Somewhere along the line someone spliced twisted pairs into station wire. Coming from the telco service you should have 4 incoming wires...red, green, black, yellow. The red and green are line 1, the black and yellow are line 2. Another approach would be...At the incoming service terminal, make note of what colors from the house wiring are going to the incoming telco service wires. Disconnect the lead where the incoming black lead is and connect it to the terminal where the incoming green is. Then disconnect the lead where the incoming yellow wire is and connect it to where the incoming red wire is. You can leave the incoming black and yellow wire connected to their existing terminals with nothing connected to them.