Issue of DRC 07 for the financial year 2019-2020

In financial year 2019-20 we claimed ITC as per supplier invoice copy
but supplier upload the wrong details in their GSTR 1
so that there is difference in GSTR 2a and GSTR 3b
department send notice for the same
I have attached the invoice and e-way bill copy while replying notice

but the department want a letter to be submitted on behalf of supplier mentioneing that he uploaded the wrong invoice

what should I do in that case