Gear problem

Hi

Thanks for letting us have the chance to ask you as expert in cars.

Automatic gear v8, 5.6 L.

I had a problem with the gear box it started to make a noise then one day the car just stuck on the third gear so when I stop you know it takes time to accelerate
Then I stopped and call the car shop and asked me to bring it next day.

So in the morning when I ride it I noticed that the car now is on four wheel drive and cannot drive faster than 60 km/h and I cannot change the mode to back wheel drive.

In the shop they opened the gear box and changed some damaged parts, and then put it back together.
On the time they want to make test drive it was the same problem exactly.

They told me they have checked it on the computer and the problem it is in the fuse box!

After I paid $600.00 now they asked me to buy fuse box!

They said fuse box is damaged and this is the automatic is not shifting.

Sorry, but is it possible that this is true?

I mean what is the relation in between?

I thank you very much and awaiting your advise.

Thanks
Sam