REFUND - REFUSAL

I bought tubes from @nick 4 months ago, I asked for an exchange, however the stock was in Kimberly, so I have to give him the new specs and I paid around R12 000 for the new items as per the client specs that I shared with him. Client returned the stock saying that its still not inline with the specs he shared with us( Nick and myself), I asked nick for a refund, he told me that he charges 35 % for all his returns mind you I had a voucher of 10 percent that I could not use from his onlineshop and he refused to credit me with the voucher that was just above R1000. Right now he is refusing to give me refund, telling that hes going to keep my money for the next purchase, I asked him what next purchase, I only wanted to purchase the centrifuges not him to hold me hostage to buy other stock from him