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Unfortunately there is no way to stop tree roots.

It is best to have the tree removed before further damage is done to your property.
https://www.gardeningknowhow.com/ornamental/trees/tgen/problem-tree-roots.htm

To much water, to often can lead to root rot quite easily with an Avocado Plant.
The small roots become overwhelmed and will die off.
Soil should be a light, loamy mix and the pot should have a good drainage hole.
You should only need to water every 2 to 3 weeks.
Never let the soil stay soggy.
Also when you water you should water until the water runs through the drainage hole, then allow any excess water to drain away. Watering to often in small amounts never allow the roots to fully take up water.

https://www.gardeningknowhow.com/special/children/sprouting-avocado-pits-how-to-root-an-avocado-seed.htm

Here are some links to help you.

http://www.ipm.ucdavis.edu/PMG/selectnewpest.avocado.html
https://www.gardeningknowhow.com/edible/fruits/avocado/avocado-pests-and-diseases.htm

Check the soil content. It is best to grow an Avocado in a clay pot with a potting mixture of soil and sand. Drainage is key to plant health.

Your plant may be showing signs of root rot.
Here is a link to refresh you on the care requirements.
https://www.gardeningknowhow.com/edible/fruits/avocado/indoor-avocado-plant-care.htm

If you have lost the leaves, you can check the stems to see if they are still alive.
If you see signs of life, they may recover.
Here is how to test your plants.

https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-scratch-test.htm
https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm

Try not to stress to much, I like to remember that a plant loss makes for an opportunity!

Unfortunately the answer is no, you cannot remove roots and solve the issue.

Avocado Trees roots are considered invasive and can greatly damage a homes foundation.

A minimum of 10 feet from any structure is recommended, although I would suggest a larger amount with some trees reaching 40 to 60 feet.

Though the decision is hard, you will only have further damage to your block wall unless you remove the tree.