Fraud by mobile repairing center

Dear Sir, My query is about fraud done by a mobile repairing center. i had a Ipad worth 56,000/- its internal memory was 128 GB, it got some problem and was unable to start i consulted to a repairing center as it was out of warranty he offered free check up. he told me that he will repair and it will cost me around 2600/- and the repair will take 2 days. i agreed and after 2 days he told we are working on it we need 2 more days. after 2 days he told we have some issue with battery shall i change the battery? i told him not to change battery and give it back to me. after that he told i have checked it myself battery is ok it has issue with display, that all discussion took 1 month. after one month he returned my Ipad it was working well but it was having only 32 GB memory instead of 128 GB. i asked him over phone and recorded the call in which he agrees that there may be a mistake. its serial number was also different from mine. finally he told me to give me another with 128 GB memory. now please help me what shall i don in that case. i bought that i pad online and i have online invoice. Thanking you....