Hello @Dylsmum woah that sounds like a nightmare! I believe I would've used a flamethrower to get rid of the spiders, hopefully, they do not return back soon.
I did bump into a post not long ago today, where the individual had a similar issue with the broadband speed, again it was due to damp weather and moist around his box, but minus the spider situation.
Little external issue like this goes unnoticed, glad to know you did think about checking your junction box to see if there were any issues you could spot. If you do find your broadband speed is still not up to scratch, let us know and we would be happy to investigate this further.