CaveDweller2 is correct, your issue is the wire itself.
To replace one simlar setup we used the existing phone wire as the pull string for new real string. Then using the new string we pulled two Cat 5's and a new pull string - always leave a string for the next pull, you never know when you will need it. We got lucky that he had buried the original cable in a conduit just big enough to fit the new cables.
We also did the wireless setup between two offices at almost 2,000 feet, but over the long term we had issues with the signal quality due to trees, vehicles and new Wifi setups in the signal path. The trick to getting it to work at that distance was the routers. We found routers with external antennas and then changed those out for some after market high gain directional antennas. Just make sure you get the right connectors for both ends and you may need to make some pig tails to connect them. New firmware also allowed us to boost the signal a little and not fry the radios. Made our nightly off site backup possible