Homeowner's Association refuses to remove trees

I live in Southern Cal.

The next door townhome project's THREE 60 FOOT pine cone trees are encroaching my property and they are causing a hazard (constant falling pine cones on my patios and front and side yards--very high traffic areas). I contacted the Homeowner's Association of the townhome project and let them know of my concerns, and I got three expert opinions (and estimates) from tree service companies on how best to solve the problem. All three experts state that the only safe way to resolve the problem is to remove the trees, because cutting them at the property line would mean cutting all the branches on my side leaving their side "side-heavy" and potentially causing the very large trees to fall. Additionally, the tree roots are causing their eight foot concrete & wood fence to lean on my property.

I notified the HOA in writing and they said they would review my request and the bids and get back with me, but they have not responded. I'm following up with another letter (certified), but if they refuse, what recourse do I have?

If I cut the branches encroaching my property, it will make their tree side-heavy. If I don't, someone cut potentially get seriously hurt on my property, not to mention, the damage the hanging branches could cause to my roof and the hassle it is to continuously pick up all the falling needles.

Please advice. Thanks.