Okash online bank app Scam

sometime in April I requested for loan of 30k to pay in 1 month, from okash app, my pastor needed it for something very emergent that morning,okash accepted the request but didn't give me the money since that morning, we later look for money elsewhere and solved the issue only for okash to send the 30k in the evening, I called them and told them we don't need the money again. they said I should send it back immediately and send them proof of payment, which I did, since that April they keep on flooding my phone with calls that I must pay interest, I tried explaining to the woman who is the customer service calling me, she didn't want to listen, when the calls became too much for complete 3nonths I began blocking the numbers, later I removed that SIM completely, then this month i put the SIM back, omor! this people continued calling, I have blocked their numbers to the extent I can't count again, I don't know whether they are using automated calls, please someone should tell me solution..... I don't owe them a dime, I sent the 30k back immediately and I sent the proof of payment to their email