The honest reply to "Why would a casino call me?" lives in the general terms. Beyond the bonus pages, every casino has general terms that govern the account itself. They decide what happens to a balance left untouched, when a bet can be voided, how much can be paid out on a single win and on what grounds the account can be closed. These clauses apply to every player, bonus or no bonus, and a few of them can cost more than any promotion.
A casino can usually close an account at its discretion, and the general terms list the grounds it relies on most: duplicate accounts, false details, suspected fraud or a breach of the terms. On closure, the balance is normally returned unless the terms allow part of it to be withheld, for instance winnings linked to a breach. A player can also close an account at any time, and the terms should explain how to withdraw the balance afterwards.
General terms allow a casino to void bets placed on an obvious error, such as odds or a payout set wrongly by mistake, often called a palpable error. A separate malfunction clause voids all pays and plays when a game fails, and the stake of the affected round is normally returned. Both clauses are meant for genuine faults, though their wording is broad. A win that is voided should come with an explanation that points to the clause and to the round in question.
General terms also limit accounts to one per person, and often one per household, address or device. They can be changed by the casino, usually with notice by email or on the site, and continued play may count as acceptance. A governing law clause names where disputes would be heard. Saving a copy of the general terms on the day an account is opened keeps a record of the version that applied from the start.
The clause names the jurisdiction whose courts would hear a dispute between the player and the casino under the general terms.
Many cap payouts per win, per day or per month; jackpot networks usually sit outside the cap, and a large ordinary win may be paid in instalments or cut.
An obvious mistake, such as odds or a payout set wrongly; general terms let the casino void bets placed on it, with an explanation pointing to the clause.
After a set period without activity, often twelve months, many casinos charge a monthly fee against the balance until it reaches zero, sometimes after one warning email.