Fault

On the 9th of August Fnb had a fault onto their system and transactions went off twice. I contacted them and they told me they’ll sort it out the next day. The next day they returned half of those transactions I further went onto calling them and they told me to fill in forms for the rest of the reversal and attach proof. How I’m I suppose to attached proof of slips I don’t have and why did they only reverse half and not the rest. I wouldn’t recommend this bank lately there’s just endless problems