Damp problem since the cavity insulation and new windows getting alot of damp condensation

Cavity insulation will only improve the wall temperature and help with condensation, so it’s not that . New windows can make the problem worse as they are totally sealed and don’t allow for even the tiniest air exchange . All the conditions you describe are from high humidity within the property . Purchase a digital thermal hygrometer off the Internet for about £18 and check the humidity , it should be 51-60%. You need to ventilate the property without lowering the temperature; do not leave windows open , this only makes it worse due to heat loss.

this could be a lot of different reasons without actually looking at the issue is impossible to say, cavity wall insulation can trap any water ingress getting into the cavity & allow it to bridge the cavity, most new windows have a security lock allowing them to open a few mm working a bit like trickle vents as long as you heating is set at the same temperature to compensate for what is being lost this would help with your condensation, it should be but is not law at the moment to only fit all new windows with trickle vents