By law, credit card providers can't contact you in any way to offer to increase your credit limit - even if you previously opted to receive these offers. This applies to both new and existing credit cards.
You can ask your card provider to increase or reduce your limit at any time (they’re required by law to do so). A provider must assess your ability to repay an increased limit within 3 years and should deny the limit if you can’t.
The provider (aka issuer) may decide to decrease your limit for various reasons, such as changes in your credit profile or creditworthiness for example.
It's important to understand that credit card limit increases or decreases are not guaranteed and are subject to the discretion of the credit card issuer.
Factors such as credit history, payment behavior, income stability, and overall creditworthiness play a role in determining credit limits. It's advisable to regularly review your credit card statements, credit reports, and communicate with the issuer to ensure that the credit limit aligns with your needs and financial goals.