These centers told you the truth.
Apple and Apple Stores and Apple authourised service centers may not/do not repair iPads.
They will ONLY offer in or out-of-warranty device replacement ONLY.
Sorry.
iPads are difficult to repair, in a timely manner,and can result in more damages caused during repairs.
Much of what it is inside of iPads is HEAVILY glued up/sealed up components that can be difficult to remove without doing damage to the exterior, aluminium back case and/or damaging many other small, finicky parts inside of the iPad, in the process.
Also, iPad repair may take much longer than most common Apple product customers/users are willing to wait.
Would you;d be willing to wait 7 days or more, without your device, waiting for it to be repaired?
Most Apple product users, today, do not really have this kind of patience to wait that long for their iPad to be repaired, if they truly need the device back ASAP.
Unlike an iPhone, which can be more quickly repaired for simple things like a battery or screen, iPads are a much more complicated device to be able to be repaired quickly.
AND, in the end, the actual repair maybe close to the same costs, OR more, than a full device replacement.