Help

Hello everyone,,
Newbie here that could do with some sound advice if you could help out?

I have been working for a particular client for nearly 7 years and, after a very good run, I have been told that my services are no longer required. I would normally just shrug my shoulders and move on, but sadly nepotism has caused our separation and it has left a bad taste in my mouth.

I have some outstanding invoices that I am about to send in to them, which they have asked for, but now they are asking for all of the previous artwork that I have produced for them… in particular a huge technical portfolio, approx 200 pages of converted CAD files and basic line illustrations.

I am quite thorough with my filing, but all the same, retrieving the artwork (approx 65gb plus 35gb of high res location photography) is going to take some serious time.

Do you think it is unreasonable to ask a fee for doing this?

I am also aware that if I give them my photographic library, then it can be used as the (ex)client sees fit. I would happily do this for an agreed fee (I am not likely to need the images ever again as they are specific to this client) but am loathed to just hand it over.

Does anyone on here know the legal position regarding this? Am i obliged to hand over the artwork as they have paid all of their invoices to date?

Am I able to ask them to desist in using any of my photography, be that in print or the interweb, until they agree a fee?

Or do I simply just have to hand it over as they own the copyright?

Your help would be greatly appreciated.