I guess the first action would be to get the money of the original repair back if they didn't do it properly. If the shop is not willing to sort this out, you should contact Brother and ask them to help, or/and consider to contact your local BBB (I think that's what it's called in the US, an organization that helps and advises when business deals go sour). Buying a new machine with embroidery capability will be expensive.
You could of course (wink, wink, tongue-in-cheek, from one mother of lively sons to another) cancel the boys' pocket money until you have enough cash to buy an all-singing, all-dancing Bernina 830.
Lorchen