UPDATE : For Your Information and to help other people who might have the same problem:
I contacted Customer Support and they canceled the original order for me.
I wrote: " I WOULD LIKE TO CANCEL AN ORIGINAL ORDER BECAUSE WE DID A CUSTOM ORDER IN PLACE.: A buyer ordered my basic gig (original order #XXXXXXXXX), but after talking with him in the chat, I made a “custom offer” to him (I used the “create an offer” button in the chat), which he accepted, and I delivered, and the buyer accepted the delivery. (Custom Order #YYYYYY)
But the original order #XXXXXXX still remains in the active orders.
So I would like to kindly ask you to cancel the original order #XXXXXXX without impacting my statistics.
Thank you.
Best regards.
Didier"
(I joined 2 screens copies of the 2 orders)
They replied: "Hello Didier,
Thank you for sharing this with me, I will gladly review the order for you and assist!
After checking this order for you, I have gone ahead and cancelled this order per your request. As for your cancellation rate, I am sure that you already know that this is an automated process that can include all cancellations in it, based on many factors. However, I have checked on this for you too, and from what I can see, it seems that this order is not impacting it.
I hope this helps. Please let me know if you need any further assistance, I would be more than happy to do so.
Best regards, "
it “seems” to not impact my statistics 
(Grammarly found and error in their reply
“cancelled”) so I think it’s not an automated reply, or they have mistakes in their automated replies?
Thanks again everyone for your help @genuineguidance @marinapomorac @auto03376212813
Have a nice day our night 