Insufficient decorative fence panels - can they be returned?

Hi, where a variety has been discontinued by one supplier, it may well still be available from another and your builder may simply not be willing to look elsewhere. If you get the name of the product you may find it in stock from another supplier. As a Landscaper if I had supplied an insufficient amount of panels and couldn't source more I would return the panels to the supplier and offer you a variety that is available. Normally merchants are pretty good with returns especially when builders often return for business. If your builder simply refuses to return them, perhaps contact the supplier and leave feedback accordingly.

responsible for the job they do

The builder may be reluctant to return them to his supplier as dime suppliers/builders merchants may charge a re-stocking charge. There are many online companies that will supply decorative panels. Just because the builders supplier has no more stock you should still be able to source matching panels. There are also suppliers that will custom manufacturer panels so with a bit of research the company that installed the fence should be able to get more panels.

Unfortunately, this question is highly invalid, as for one thing I personally do not get involved with boundary fencing issues especially where neighbours cannot agree amicably with solutions, and also as it is encumbent upon individual neighbours to be responsible for boundary fencing to the right hand side looking outwardly from the front and rear elevations. It is not clear from this particular description how this is occurring but without considering any of this it is simply not worth becoming involved in issues where works have nor or cannot apparently be completed especially for the reasons you put forward. However, if you can reasonably negotiate this with your neighbours then I'm sure a solution will be mutually and conveniently available. Common agreement is crucial in such matters. Sorry to be non-committal on this occasion but in my considerable experience due caution and consideration of all factors is paramount. For your further assistance, however, I will add that other comments are very much appropriate, and also it might be possible to have a matching panel(s) made up and fitted, an experienced and competent carpenter should be able to accomplish this, but, please - by common agreement in everybody's interest.