Where is the car?
Did they rent it to you in Sweden?
The reason you are experiencing delay is that you keep posting before I have responded which pushes the question to the back of my list.
Were you allowed to remove the car from the country?
You need to check your contract. However, I would imagine that you are not allowed to remove the car from the UK.
If you have done so and are not paying then that is something that they could report to the police.
Whether the police would act with you in Sweden is another matter.
But certainly in academic law it is an offence.
Can I clarify anything for you?
P.S. - I am just about to travel home so may not be able to respond immediately.
I haven't offered a call.
I think that it is the site automating an offer.
If you returned it to their offices in the UK I'm sure that would be acceptable.