Letter of Credit Forum

We have received a set of dox for bill of collection with an instruction to deliver to client against aval/guarantee of payment by the receiving bank. Unfortunately, dox have been delivered against normal acceptance to client and we send MT 412 stating that Drawee has accepted this collection without any responsibility or guarantee on our part to pay on maturity date xxxxxx.The Sender Bank have not comments on the message or highlighted that it is against aval. After 20 days from maturity we have received an amendment to reduce the bill amount from USDxxxxxxx to USDxxxxxxxxxxxxx. After that we received so many tracers regarding the above bill for payment. The sender bank is asking for the payment based on their aval instruction while we as a collecting bank stating we have commented an error at the beginning but the sender have not refuse or ask for correction. Does the sender bank have the right to ask for payment from the collecting bank?

Thanks