If there is a dispute over property that arises from a failed relationship the best way to resolve this is via a solicitor and/or the courts who can make an agreement or ruling on what items each person can take.
Often the police are called after an argument has taken place when one party goes to take items that they believe are theirs from a former address, hoping that the police will be able to order their former partner to hand them over. This is not the case, the police have no power to enforce the return of property under these circumstances.
The police can only mediate and hopefully agree the return of personal items such as clothing, jewellery or personal papers, even if you are in possession of receipts or other paperwork that you believe gives you a claim or title to those items.
Sometimes a mutual friend or relative can undertake this mediation on your behalf and come to a compromise until the situation can be fully resolved without the police being called, which can sometimes aggravate the situation.
In law if there is a dispute over ownership of property under such circumstances it is usual that neither party can dispose of these items, by selling them or giving them away until the dispute is resolved - so your former partner cannot dispose of items you believe to be yours. However each case is different and you should take specialist advice on this subject from a solicitor to make sure this applies to your case.