Frankly, this makes my blood boil. Full disclosure: I used to work at Sendgrid's competitor (Mailgun) and I'm quite familiar with what's happening under the hood. You allowed spam to be sent from your account. You poisoned the IP space (not just one address you were sending from, but the IP block, affecting others) with spammy reputation. These blocks are expensive and hard to acquire (due to IPv4 shortage) and at this point you have caused more damage to Sendgrid and their customers, than your account value can probably compensate for. What kind of "support" do you expect at this point? You rented a hotel room, gave the key to someone who erected a meth lab there, and you're unhappy with the hotel's reaction?
Sending email on behalf of other people is hard work. The margins are not great, the ratio of spam-to-ham for new accounts is insane, and they're constantly under pressure between their customers who pay very little but want to spam the entire universe (I am sorry but most of you do!) and ESPs not wanting that traffic.