Point is, everything was working fine, then things got really bad (from almost 100% to barely 10%) when looking at all the pieces,
its (your domain - places where you build links - indexer - search engine) .. I thought it was due to your domain being flagged or something, so anything with your url in it wont get indexed, or it was google all along.. but according to the information you supplied (Written on their website that something is wrong) I think its them alright. but the thing is, you tried other indexers so, back to square one i guess?
Remember that over 90% of indexing services are no longer effective as they used to use old methods for indexing the links that no longer work, but they are happy taking your money and give you little or mostly nothing in return. so there is also that. maybe use another reputable indexing service... https://www.blackhatworld.com/seo/99-of-indexing-services-are-a-scam.1121676/ Maybe this will help you choose a better indexing service and see if something changes with indexing rate. Good luck.