Unfortunately, without the additional information requested in my first/previous response, I will not be able to give you detailed advice to your question, but I will be able to give you a general answer, which I hope will be of assistance. If you are able to supply the additional information later, please do so and I will then come back to you with a more detailed answer.
Police can use force to gain entry for a number of reasons particularly where they think an offence may be being committed or someone is in danger etc.
You say that police say someone saw you naked in front of your window some days before. If that were the case and when police arrived to your property that should not give then grounds to force entry unless there is more to the matter than explained here.
Even if you were seen through a window naked, that in itself is not an offence. However, if it is done deliberately to cause alarm or distress to neighbours who may see you then it does become an offence of exposure.
I cannot expand further on that without knowing more on the circumstances.
As foreign released by police "under investigation" this means that you have not been charged with any offence and have not been released on police bail. But it does mean that the police may continue any investigations in their own time, without time constraints of police bail getting n the way.
There is no time limit for how long this can or would last. Because there is no bail, the police can take as long as required and if they need to speak to you again, they may ask you to attend the station.