Have you put the old hard drive in a USB enclosure and attached while booted with the SSD?
You should be able to see the hard drive then and copy your data off. If it doesn't show up you need to decide how important the data is and whether or not you are willing to pay several hundreds of dollars minimum to get your data back. If you are never going to pay that, then there is software out there that might be able to recover your data. Getdataback is one, or iCare data recovery, there are a lot. I usually use the free version to see if it can see the data and then buy the license to recover it.