Facts
The appellant [A.] had initiated debt collection proceedings against [B.] . In the context of these debt collection proceedings, the Weesen-Amden debt collection office seized on 7 April 2011 the share belonging to the debtor [B.] in the simple partnership Baukonsortium [B.] -[C.] -[D.] . On 21 May 2012, [A.] filed the realisation request. The single judge at the District Court of See-Gaster ordered on 5 July 2013 the realisation of the seized share through dissolution and liquidation of the simple partnership. As an amicable agreement with the partners on 27 February 2014 failed to materialise, the debt collection office offered [A.] the assignment of the debtor's share in the partnership, which he did not make use of. Subsequently, on 4 July 2014, the seized share was auctioned, with [A.] receiving the award for CHF 13,000.--.
On 6 November 2014, the debt collection office prepared the collocation plan and the distribution list. As a claim of [A.] , it collated the amount, including interest and costs, of a total of CHF 164,100.10. From the realisation proceeds (liquidation share), it allocated [A.] a net amount of CHF 98,085.--. A certificate of loss should be issued to him for the remaining claim of CHF 66,015.10.
[B.] unsuccessfully filed a complaint against the collocation plan and the distribution list with the lower supervisory authority. On his appeal, the Cantonal Court of St. Gallen, the upper supervisory authority for debt collection, annulled on 11 May 2015 the collocation plan and the distribution list and remanded the matter to the debt collection office for further consideration in accordance with the considerations. The upper supervisory authority held in the judgment that the auction proceeds of CHF 13,000.-- (less realisation costs) were to be distributed and that a certificate of loss was to be issued to the creditor (over the uncovered claim). However, the payment of CHF 103,310.10 by the Canton of Valais to the debt collection office concerned the relationship between the simple partnership and the Canton of Valais. It was the responsibility of the debt collection office "to make arrangements with the Canton of Valais regarding any possible reimbursement of the amount".
Thereupon, [A.] approached the debt collection office and demanded - with reference to an agreement with [B.] - the reimbursement of the amount of CHF 103,310.10, which the Canton of Valais had transferred to the debt collection office as a fee for the construction consortium. By order of 26 June 2015, the debt collection office did not comply with these requests and, with reference to the considerations of the upper supervisory authority in the judgment of 11 May 2015, insisted on repaying the amount to the Canton of Valais.
[A.] unsuccessfully filed a complaint against this order with the lower supervisory authority. The upper supervisory authority also dismissed his complaint on 13 September 2015.
Considerations
The Federal Court concluded that the appellant [A.] is not entitled, on the basis of the assignment he has claimed, to have the…