Help, I can't get my A-level certificates

For health reasons and personal reasons, I wasn't able to collect my certificates. I was however fully in contact with my sixth form about my situation and we agreed that we could find an arrangement for them to post my certificates. It hasn't been 18 months and they are blaming me that I should have collected them sooner. I have proof of many emails about my situation and for them to agree to cooperate. I've also called them so many times about it in previous times, I've left my name and my contact details again so many times.
I think what happened is that they forgot about me and they didn't care at all. I don't know what to do. I've tried to do other arrangements but I can't afford to buy the replacements. I am not economically stable.
I don't know what to do? I was thinking to provide more evidence that it wasn't my fault, so I was wondering if there are any guidelines for schools keeping call history... GDPR?

By the way, I am also applying for uni this year and the main person that I kept in contact about my certificates is my sixth form tutor which is my current referee and the main office of my school. I have already applied unis and I am still waiting for any offers, if I take this further do you think this is gonna ruin my reference?

Any advice would be nice.
Thank you

Are you saying your school has lost/destroyed your certificates? Did you sit the exams in May/June 2018?

Yes. I sat my exams in May/June 2017. They told me they only keep unclaimed certificates up to 18 months. This doesn't even make sense because it hasn't been 18 months and I have several emails from 2017 and 2018 regarding this issue. I asked and agreed for any arrangements and they confirmed it.

Well if they are lost/mislaid all you can really do is order new ones from the exam board(s).

You can then try claiming the cost back from school. But 17 August 2017 to today is (just) over 18 months so I doubt you have much chance unless you have an email proving they said they would keep them longer.

I think I am gonna claim the costs. I didn't count from August, I know that the certificates arrive 6 weeks after results day but for my sixth form didn't have the certificates until much later. So I emailed them and called in November 2017 and what they told once that they receive the certificates it will get posted. Since then I kept emailing them. Should I pursue legal action, report them? The thing is I kept my communication whereas the school didn't