Depends what bit of the Caliper is broken. It is easy to say it was working fine before he touched it so he needs to fix it but he is likely to tell you where to go. You now have choices
1. You can believe him and pay up for a new caliper.
2. tell him he broke it and give him a chance to fix it. you will need to do this in writing so you can prove you gave him a chance if he tells you to do one.
3.take it somewhere that will confirm it was broken by him and give him a last chance to fix it. Good luck though, I think you will struggle to get someone and it may cost more than getting it fixed.
4. Do number 3 then get it fixed elsewhere and take him to small claims court.
5. Just get it done elsewhere. Here is a link to a refurbished caliper for £90. Double check it is the right one.
https://www.ebay.co.uk/itm/O-E-Volvo...UAAOSw9NdXwtGT