Neighbour had extension now I’ve got damp in adjourning corner

Hi there, I would suggest speaking to your neighbour again - you have a signed party wall agreement and if the problem was caused by their work, then they will have to put it right. Make a written note of what was said and when (just in case you need to go to court later) Then write a letter to them, again setting out the issues. Speak to your insurance company - you may have legal cover as part of your building insurance and if you make a claim, they could seek to get the money from your neighbours. You might need to engage a surveyor (one who is experienced with party wall issues) to asses and report on the findings. Hope that helps and good luck.