Spray WD into the locks, I'd say leave it overnight but you may not have time, so just turn the key gently until it turns the lock, not just the barrel. Bear in mind that the barrel could now be upside-down and they don't work that way even if they're nice and slick, so you'll have to try both ways. I reckon, with some patience, you'll get there.
The plip will need coding to the BSI with the number on the key card the customer has probably lost. But you'll still need to get into the car to start with.
Tip the key slightly upwards when you turn it and it may work.
The barrel is designed to spin freely if its the wrong key so it can't be forced - although this backfires if the barrel is slightly worn and you are using the right key..
2003 2.2hdi estate - mine 1998 Volvo 940 auto estate - also mine 2019 Citroen C3 something - the wife's PP2000 user, can help with faults / diagnostics in the Bournemouth area.
Just check that you have the correct key as you may have had another key from another car thrown around. As the others have said you should be able to open car with a bit of patience. Its unsual for all three barrels to be going around and the remote to stop working. Just check that there is not another key for opening the doors on the key ring.
