my site was hacked, now permissions are messed up

My website was hacked, don’t know how, but now there are links to how to get 1 million you tube views on my pages, but I dont see it in my page code.

also, if my URLs end in slash, I get permission errors, ex:

https://marylandroofingassociation.com/commercial-estimates/
doesnt work but

https://marylandroofingassociation.com/commercial-estimates
does work.

any ideas to help me get back to normal??

Thanks,
Bernie