That sounds like a problem with the DTMF decoder in the ATA rather than a problem with Asterisk. Asterisk is completely out of the loop with digit decoding until the ATA send the call to Asterisk.
DTMF is not used to establish a call between the ATA and Asterisk. Generally, the ATA would gather digits from the analog side, perform some sort of routing internally, and send a SIP INVITE to asterisk contain digits in the “To” header of the SIP INVITE.
So, if Asterisk is receiving an incorrect number in a SIP call it is not the fault of Asterisk at all. I would say that the DTMF on the Analog side of the ATA is somehow distorted causing the ATA to mis-interpret the DTMF. Some ATAs have have an input gain setting that can be tweaked to make up for this.
Suffice it to say, I would be look at that ATA and/or the analog line itself.