Nightmare with Dryden Fairfax/Erudio re. student loan

Hi all,
I had a student loan from the 90’s. I deferred as my salary was low. In 2016, I started getting debt collection letters from Dryden Fairfax – I had no idea Erudio had taken over the student loan. I never received any previous communication from SLC or Erudio about the changes. 
In 2018 and 2019, I wrote to them saying I never received correspondence from Erudio about all the changes, the option to defer, etc.
Recently, Dryden replied with copies of letters informing me of the changes and a “letter” with an option to defer. Some of these look fake.
I  recently looked at my SLC account online ( it has letters uploaded to my account), and they sent me an end-of-deferment pack at the end of 2013 to the correct address (where I was living at the time). however, the copy of the SLC letter that Dryden recently sent me (dated 20/3/2014) has a very old address from 2001/2002 – so it looks like a fake letter; also, that letter isn’t uploaded to my SLC online account. Is it worth checking this with SLC? 
Also, Dryden sent me a copy of the LETTER OF ASSIGNMENT from Erudio – dated the same date as the “fake” letter from SLC (20/3/2014). Also, with the old address from 2001/2002 -, it is very odd, especially if SLC sent me a genuine letter to my address at the end of 2013. Surely, I would have received something to the correct address. 
In 2017 – 20th April – I stupidly paid £25 to fend them away. I also now realise 6 years have passed between the last acknowledgement of the debt and the current date.
Can I send them a statute-barred letter? 
Many thanks,