What should a bank teller do if his sponsor refuses to transfer his sponsorship to an Islamic bank and refuses to cancel his residency permit or give him a no-objection certificate, after seven years of work and a change in the sponsor's treatment?

The contract is the law between the contracting parties, as long as it does not violate the Shari'ah. Violating its terms is a forbidden injustice if it leads to the loss of a right or harm. If the contract between you and your employer obliges him not to work for anyone else or to return you to your place, then he is not obliged to agree to the transfer of sponsorship or an increase in salary. If you do not wish to renew after the contract expires, you are not obliged to renew, and the matter can be resolved with wisdom. However, if the contract implies your right to move to another (employer), then he has no right to prevent you.