My husband I returned a vehicle to a finance company 12 years ago and are now having my husbands wages garnished for 25% of his pay every week to pay the debt. Is this legal because we agreed to pay $50 a week 7 years ago?

In order from a garnishment to take affect it had to have went through the court. Did you get your agreement in writing? Also did you receive a court date? If you did and you ignored it then a default judgement most likely was entered depending on what state you are in judgements can and are often renewed

Did you pay the $50 a week, every week, for the past 7 years?

I would guess that answer is no.

You had to be sued for a garnishment to be in effect, and you have interest that has accrued for the past 12 years to cover as well as any court costs and legal fees.

Unless you can prove that you were never legally served notice of the suit, his check will be short for quite some time I'm afraid.