Skip talking to the Sales people. Ask to see the department manager or even the store manager. Make an appointment if necessary. It will probably have to be at his/her convenience. (First, you need to talk to the 'right' folks.)
If this doesn't work, ask the manager who you can write to to complain. Then send the letter. In the mean time, you can write to Consumer Reports and tell them your problem. They may have some info for you in terms of how to get it fixed or who to write to. They have a large resource of information!
And my last, free, unsolicited advice is not to buy their lawn and garden 'stuff' that is gas or electrical. (I know I'm probably gonna get some flack on this but no one's gonna change my mind.) Sear's tools such as Craftsman and their Lifetime Warranty is what got them such a good reputation years ago. They've ridden that wave too long. Most of their mowers and such have plastic gears and cheap parts. And, try to buy a replacement part for this stuff any place else but Sears. You can't. It's almost their policy to contract with a company that makes mowers and stuff, and have some things 'changed' so that the consumer HAS to ctc Sears for replacemen parts. I don't know how much you paid for your mower but it wasn't much I'm sure. Here's a suggestion. If you have to buy a new mower, go ask a landscaper that's out in the field if he/she has a recommendation for one. If he/she says Sears, then you know you're bothering them. Ask for a 2nd and 3rd choice because you don't want a Sears. I've learned the hard way. If you want good lawn equipment, ask a landscaper. If you want a good power saw or drill, ask a carpenter. And if you want reliable legal advice, ask a lawyer! I think you know what I'm trying to say. 'nough said.
I wish you well. If you get a chance, post a message to let us all know how you made out.