I feel for you. I had similar experience bought some bobbins for the machine and found they were the wrong size so swung past the store since I was in the area but didn't have my receipt but because I did't have my receipt they gave me a credit for $2.-- and when I got home saw I had paid over $5. something boy I was really upset. You have my sympathy.
I avoid that place usually but this was a big mistake.