Insurance claim blocked septic drain in neighbours garden

F8photo

Hi,
We have discovered that out septic tank drain goes under the fence into a neighbours garden and joins into theirs. This then goes down their garden and originally would have gone into a field ditch. Our neighbour has had a treatment plant put in under his insurance as it was blocked with roots. [I would think the original drains were done when our property was built in the mid 1960's].
When the drain guys were next door they said they had damaged our joint drain and water seemed to be flowing, by now my neighbour no longer used the original sewer pipe as they put a new discharge pipe in from the treatment plant.
Ours used to work in the summer but it no longer does, we have a pump system and land drains in our garden for winter.
Would I have a claim do you think, we are covered for drains. They are the salt glaze type, not fibre.