The financial value of the previous loss was €5249, of which the OP was his/her own insurer for the first €250 of the loss. In my opinion, the previous claim was settled for an amount of €5249, less the excess and not for an amount of €4999. Therefore, the value of the previous claim should be disclosed at the gross amount, prior to deduction of the excess.
However, the only opinion that matters in determining whether the previous loss was €5249 or €4999, is that of the underwriter who will decide whether or not to accept the risk. What I would suggest to the OP is that he/she contacts a broker who will plead the case and hopefully get cover. The other alternative is to go to the lending institution ( if indeed there is one) and they should be able to influence an insurer with which they have a standing relationship, to take the risk.